/**
 * Compiler implementation of the
 * $(LINK2 http://www.dlang.org, D programming language).
 *
 * Template implementation.
 *
 * Copyright:   Copyright (c) 1999-2017 by Digital Mars, All Rights Reserved
 * Authors:     $(LINK2 http://www.digitalmars.com, Walter Bright)
 * License:     $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
 * Source:      $(DMDSRC _dtemplate.d)
 */

module ddmd.dtemplate;

import core.stdc.stdio;
import core.stdc.string;
import ddmd.aggregate;
import ddmd.aliasthis;
import ddmd.arraytypes;
import ddmd.attrib;
import ddmd.dcast;
import ddmd.dclass;
import ddmd.declaration;
import ddmd.dmangle;
import ddmd.dmodule;
import ddmd.dscope;
import ddmd.dsymbol;
import ddmd.errors;
import ddmd.expression;
import ddmd.func;
import ddmd.globals;
import ddmd.hdrgen;
import ddmd.id;
import ddmd.identifier;
import ddmd.init;
import ddmd.mtype;
import ddmd.opover;
import ddmd.root.aav;
import ddmd.root.outbuffer;
import ddmd.root.rootobject;
import ddmd.tokens;
import ddmd.visitor;

//debug = FindExistingInstance; // print debug stats of findExistingInstance
private enum LOG = false;

enum IDX_NOTFOUND = 0x12345678;

/********************************************
 * These functions substitute for dynamic_cast. dynamic_cast does not work
 * on earlier versions of gcc.
 */
extern (C++) Expression isExpression(RootObject o)
{
    //return dynamic_cast<Expression *>(o);
    if (!o || o.dyncast() != DYNCAST.expression)
        return null;
    return cast(Expression)o;
}

extern (C++) Dsymbol isDsymbol(RootObject o)
{
    //return dynamic_cast<Dsymbol *>(o);
    if (!o || o.dyncast() != DYNCAST.dsymbol)
        return null;
    return cast(Dsymbol)o;
}

extern (C++) Type isType(RootObject o)
{
    //return dynamic_cast<Type *>(o);
    if (!o || o.dyncast() != DYNCAST.type)
        return null;
    return cast(Type)o;
}

extern (C++) Tuple isTuple(RootObject o)
{
    //return dynamic_cast<Tuple *>(o);
    if (!o || o.dyncast() != DYNCAST.tuple)
        return null;
    return cast(Tuple)o;
}

extern (C++) Parameter isParameter(RootObject o)
{
    //return dynamic_cast<Parameter *>(o);
    if (!o || o.dyncast() != DYNCAST.parameter)
        return null;
    return cast(Parameter)o;
}

/**************************************
 * Is this Object an error?
 */
extern (C++) bool isError(RootObject o)
{
    Type t = isType(o);
    if (t)
        return (t.ty == Terror);
    Expression e = isExpression(o);
    if (e)
        return (e.op == TOKerror || !e.type || e.type.ty == Terror);
    Tuple v = isTuple(o);
    if (v)
        return arrayObjectIsError(&v.objects);
    Dsymbol s = isDsymbol(o);
    assert(s);
    if (s.errors)
        return true;
    return s.parent ? isError(s.parent) : false;
}

/**************************************
 * Are any of the Objects an error?
 */
extern (C++) bool arrayObjectIsError(Objects* args)
{
    for (size_t i = 0; i < args.dim; i++)
    {
        RootObject o = (*args)[i];
        if (isError(o))
            return true;
    }
    return false;
}

/***********************
 * Try to get arg as a type.
 */
extern (C++) Type getType(RootObject o)
{
    Type t = isType(o);
    if (!t)
    {
        Expression e = isExpression(o);
        if (e)
            t = e.type;
    }
    return t;
}

extern (C++) Dsymbol getDsymbol(RootObject oarg)
{
    //printf("getDsymbol()\n");
    //printf("e %p s %p t %p v %p\n", isExpression(oarg), isDsymbol(oarg), isType(oarg), isTuple(oarg));
    Dsymbol sa;
    Expression ea = isExpression(oarg);
    if (ea)
    {
        // Try to convert Expression to symbol
        if (ea.op == TOKvar)
            sa = (cast(VarExp)ea).var;
        else if (ea.op == TOKfunction)
        {
            if ((cast(FuncExp)ea).td)
                sa = (cast(FuncExp)ea).td;
            else
                sa = (cast(FuncExp)ea).fd;
        }
        else if (ea.op == TOKtemplate)
            sa = (cast(TemplateExp)ea).td;
        else
            sa = null;
    }
    else
    {
        // Try to convert Type to symbol
        Type ta = isType(oarg);
        if (ta)
            sa = ta.toDsymbol(null);
        else
            sa = isDsymbol(oarg); // if already a symbol
    }
    return sa;
}

private Expression getValue(ref Dsymbol s)
{
    Expression e = null;
    if (s)
    {
        VarDeclaration v = s.isVarDeclaration();
        if (v && v.storage_class & STCmanifest)
        {
            e = v.getConstInitializer();
        }
    }
    return e;
}

/***********************
 * Try to get value from manifest constant
 */
private Expression getValue(Expression e)
{
    if (e && e.op == TOKvar)
    {
        VarDeclaration v = (cast(VarExp)e).var.isVarDeclaration();
        if (v && v.storage_class & STCmanifest)
        {
            e = v.getConstInitializer();
        }
    }
    return e;
}

private Expression getExpression(RootObject o)
{
    auto s = isDsymbol(o);
    return s ? .getValue(s) : .getValue(isExpression(o));
}

/******************************
 * If o1 matches o2, return true.
 * Else, return false.
 */
private bool match(RootObject o1, RootObject o2)
{
    enum debugPrint = 0;

    static if (debugPrint)
    {
        printf("match() o1 = %p %s (%d), o2 = %p %s (%d)\n",
            o1, o1.toChars(), o1.dyncast(), o2, o2.toChars(), o2.dyncast());
    }

    /* A proper implementation of the various equals() overrides
     * should make it possible to just do o1.equals(o2), but
     * we'll do that another day.
     */
    /* Manifest constants should be compared by their values,
     * at least in template arguments.
     */

    if (auto t1 = isType(o1))
    {
        auto t2 = isType(o2);
        if (!t2)
            goto Lnomatch;

        static if (debugPrint)
        {
            printf("\tt1 = %s\n", t1.toChars());
            printf("\tt2 = %s\n", t2.toChars());
        }
        if (!t1.equals(t2))
            goto Lnomatch;

        goto Lmatch;
    }
    if (auto e1 = getExpression(o1))
    {
        auto e2 = getExpression(o2);
        if (!e2)
            goto Lnomatch;

        static if (debugPrint)
        {
            printf("\te1 = %s '%s' %s\n", e1.type.toChars(), Token.toChars(e1.op), e1.toChars());
            printf("\te2 = %s '%s' %s\n", e2.type.toChars(), Token.toChars(e2.op), e2.toChars());
        }

        // two expressions can be equal although they do not have the same
        // type; that happens when they have the same value. So check type
        // as well as expression equality to ensure templates are properly
        // matched.
        if (!e1.type.equals(e2.type) || !e1.equals(e2))
            goto Lnomatch;

        goto Lmatch;
    }
    if (auto s1 = isDsymbol(o1))
    {
        auto s2 = isDsymbol(o2);
        if (!s2)
            goto Lnomatch;

        static if (debugPrint)
        {
            printf("\ts1 = %s \n", s1.kind(), s1.toChars());
            printf("\ts2 = %s \n", s2.kind(), s2.toChars());
        }
        if (!s1.equals(s2))
            goto Lnomatch;
        if (s1.parent != s2.parent && !s1.isFuncDeclaration() && !s2.isFuncDeclaration())
            goto Lnomatch;

        goto Lmatch;
    }
    if (auto u1 = isTuple(o1))
    {
        auto u2 = isTuple(o2);
        if (!u2)
            goto Lnomatch;

        static if (debugPrint)
        {
            printf("\tu1 = %s\n", u1.toChars());
            printf("\tu2 = %s\n", u2.toChars());
        }
        if (!arrayObjectMatch(&u1.objects, &u2.objects))
            goto Lnomatch;

        goto Lmatch;
    }
Lmatch:
    static if (debugPrint)
        printf("\t. match\n");
    return true;

Lnomatch:
    static if (debugPrint)
        printf("\t. nomatch\n");
    return false;
}

/************************************
 * Match an array of them.
 */
private int arrayObjectMatch(Objects* oa1, Objects* oa2)
{
    if (oa1 == oa2)
        return 1;
    if (oa1.dim != oa2.dim)
        return 0;
    immutable oa1dim = oa1.dim;
    auto oa1d = (*oa1).data;
    auto oa2d = (*oa2).data;
    for (size_t j = 0; j < oa1dim; j++)
    {
        RootObject o1 = oa1d[j];
        RootObject o2 = oa2d[j];
        if (!match(o1, o2))
        {
            return 0;
        }
    }
    return 1;
}

/************************************
 * Return hash of Objects.
 */
private hash_t arrayObjectHash(Objects* oa1)
{
    import ddmd.root.hash : mixHash;

    hash_t hash = 0;
    foreach (o1; *oa1)
    {
        /* Must follow the logic of match()
         */
        if (auto t1 = isType(o1))
            hash = mixHash(hash, cast(size_t)t1.deco);
        else if (auto e1 = getExpression(o1))
            hash = mixHash(hash, expressionHash(e1));
        else if (auto s1 = isDsymbol(o1))
        {
            auto fa1 = s1.isFuncAliasDeclaration();
            if (fa1)
                s1 = fa1.toAliasFunc();
            hash = mixHash(hash, mixHash(cast(size_t)cast(void*)s1.getIdent(), cast(size_t)cast(void*)s1.parent));
        }
        else if (auto u1 = isTuple(o1))
            hash = mixHash(hash, arrayObjectHash(&u1.objects));
    }
    return hash;
}


/************************************
 * Computes hash of expression.
 * Handles all Expression classes and MUST match their equals method,
 * i.e. e1.equals(e2) implies expressionHash(e1) == expressionHash(e2).
 */
private hash_t expressionHash(Expression e)
{
    import ddmd.root.ctfloat : CTFloat;
    import ddmd.root.hash : calcHash, mixHash;

    switch (e.op)
    {
    case TOKint64:
        return cast(size_t) (cast(IntegerExp)e).getInteger();

    case TOKfloat64:
        return CTFloat.hash((cast(RealExp)e).value);

    case TOKcomplex80:
        auto ce = cast(ComplexExp)e;
        return mixHash(CTFloat.hash(ce.toReal), CTFloat.hash(ce.toImaginary));

    case TOKidentifier:
        return cast(size_t)cast(void*) (cast(IdentifierExp)e).ident;

    case TOKnull:
        return cast(size_t)cast(void*) (cast(NullExp)e).type;

    case TOKstring:
        auto se = cast(StringExp)e;
        return calcHash(se.string, se.len * se.sz);

    case TOKtuple:
    {
        auto te = cast(TupleExp)e;
        size_t hash = 0;
        hash += te.e0 ? expressionHash(te.e0) : 0;
        foreach (elem; *te.exps)
            hash = mixHash(hash, expressionHash(elem));
        return hash;
    }

    case TOKarrayliteral:
    {
        auto ae = cast(ArrayLiteralExp)e;
        size_t hash;
        foreach (i; 0 .. ae.elements.dim)
            hash = mixHash(hash, expressionHash(ae.getElement(i)));
        return hash;
    }

    case TOKassocarrayliteral:
    {
        auto ae = cast(AssocArrayLiteralExp)e;
        size_t hash;
        foreach (i; 0 .. ae.keys.dim)
            // reduction needs associative op as keys are unsorted (use XOR)
            hash ^= mixHash(expressionHash((*ae.keys)[i]), expressionHash((*ae.values)[i]));
        return hash;
    }

    case TOKstructliteral:
    {
        auto se = cast(StructLiteralExp)e;
        size_t hash;
        foreach (elem; *se.elements)
            hash = mixHash(hash, elem ? expressionHash(elem) : 0);
        return hash;
    }

    case TOKvar:
        return cast(size_t)cast(void*) (cast(VarExp)e).var;

    case TOKfunction:
        return cast(size_t)cast(void*) (cast(FuncExp)e).fd;

    default:
        // no custom equals for this expression
        assert((&e.equals).funcptr is &RootObject.equals);
        // equals based on identity
        return cast(size_t)cast(void*) e;
    }
}

RootObject objectSyntaxCopy(RootObject o)
{
    if (!o)
        return null;
    if (Type t = isType(o))
        return t.syntaxCopy();
    if (Expression e = isExpression(o))
        return e.syntaxCopy();
    return o;
}

extern (C++) final class Tuple : RootObject
{
    Objects objects;

    // kludge for template.isType()
    override DYNCAST dyncast() const
    {
        return DYNCAST.tuple;
    }

    override const(char)* toChars()
    {
        return objects.toChars();
    }
}

struct TemplatePrevious
{
    TemplatePrevious* prev;
    Scope* sc;
    Objects* dedargs;
}

/***********************************************************
 */
extern (C++) final class TemplateDeclaration : ScopeDsymbol
{
    TemplateParameters* parameters;     // array of TemplateParameter's
    TemplateParameters* origParameters; // originals for Ddoc

    Expression constraint;

    // Hash table to look up TemplateInstance's of this TemplateDeclaration
    TemplateInstance[TemplateInstanceBox] instances;

    TemplateDeclaration overnext;       // next overloaded TemplateDeclaration
    TemplateDeclaration overroot;       // first in overnext list
    FuncDeclaration funcroot;           // first function in unified overload list

    Dsymbol onemember;      // if !=null then one member of this template

    bool literal;           // this template declaration is a literal
    bool ismixin;           // template declaration is only to be used as a mixin
    bool isstatic;          // this is static template declaration
    Prot protection;

    // threaded list of previous instantiation attempts on stack
    TemplatePrevious* previous;

    extern (D) this(Loc loc, Identifier id, TemplateParameters* parameters, Expression constraint, Dsymbols* decldefs, bool ismixin = false, bool literal = false)
    {
        super(id);
        static if (LOG)
        {
            printf("TemplateDeclaration(this = %p, id = '%s')\n", this, id.toChars());
        }
        version (none)
        {
            if (parameters)
                for (int i = 0; i < parameters.dim; i++)
                {
                    TemplateParameter tp = (*parameters)[i];
                    //printf("\tparameter[%d] = %p\n", i, tp);
                    TemplateTypeParameter ttp = tp.isTemplateTypeParameter();
                    if (ttp)
                    {
                        printf("\tparameter[%d] = %s : %s\n", i, tp.ident.toChars(), ttp.specType ? ttp.specType.toChars() : "");
                    }
                }
        }
        this.loc = loc;
        this.parameters = parameters;
        this.origParameters = parameters;
        this.constraint = constraint;
        this.members = decldefs;
        this.literal = literal;
        this.ismixin = ismixin;
        this.isstatic = true;
        this.protection = Prot(PROTundefined);

        // Compute in advance for Ddoc's use
        // https://issues.dlang.org/show_bug.cgi?id=11153: ident could be NULL if parsing fails.
        if (members && ident)
        {
            Dsymbol s;
            if (Dsymbol.oneMembers(members, &s, ident) && s)
            {
                onemember = s;
                s.parent = this;
            }
        }
    }

    override Dsymbol syntaxCopy(Dsymbol)
    {
        //printf("TemplateDeclaration.syntaxCopy()\n");
        TemplateParameters* p = null;
        if (parameters)
        {
            p = new TemplateParameters();
            p.setDim(parameters.dim);
            for (size_t i = 0; i < p.dim; i++)
                (*p)[i] = (*parameters)[i].syntaxCopy();
        }
        return new TemplateDeclaration(loc, ident, p, constraint ? constraint.syntaxCopy() : null, Dsymbol.arraySyntaxCopy(members), ismixin, literal);
    }

    override void semantic(Scope* sc)
    {
        static if (LOG)
        {
            printf("TemplateDeclaration.semantic(this = %p, id = '%s')\n", this, ident.toChars());
            printf("sc.stc = %llx\n", sc.stc);
            printf("sc.module = %s\n", sc._module.toChars());
        }
        if (semanticRun != PASSinit)
            return; // semantic() already run
        semanticRun = PASSsemantic;

        // Remember templates defined in module object that we need to know about
        if (sc._module && sc._module.ident == Id.object)
        {
            if (ident == Id.RTInfo)
                Type.rtinfo = this;
        }

        /* Remember Scope for later instantiations, but make
         * a copy since attributes can change.
         */
        if (!this._scope)
        {
            this._scope = sc.copy();
            this._scope.setNoFree();
        }

        parent = sc.parent;
        protection = sc.protection;
        isstatic = toParent().isModule() || (_scope.stc & STCstatic);

        if (!isstatic)
        {
            if (auto ad = parent.pastMixin().isAggregateDeclaration())
                ad.makeNested();
        }

        // Set up scope for parameters
        auto paramsym = new ScopeDsymbol();
        paramsym.parent = parent;
        Scope* paramscope = sc.push(paramsym);
        paramscope.stc = 0;

        if (global.params.doDocComments)
        {
            origParameters = new TemplateParameters();
            origParameters.setDim(parameters.dim);
            for (size_t i = 0; i < parameters.dim; i++)
            {
                TemplateParameter tp = (*parameters)[i];
                (*origParameters)[i] = tp.syntaxCopy();
            }
        }

        for (size_t i = 0; i < parameters.dim; i++)
        {
            TemplateParameter tp = (*parameters)[i];
            if (!tp.declareParameter(paramscope))
            {
                error(tp.loc, "parameter '%s' multiply defined", tp.ident.toChars());
                errors = true;
            }
            if (!tp.semantic(paramscope, parameters))
            {
                errors = true;
            }
            if (i + 1 != parameters.dim && tp.isTemplateTupleParameter())
            {
                error("template tuple parameter must be last one");
                errors = true;
            }
        }

        /* Calculate TemplateParameter.dependent
         */
        TemplateParameters tparams;
        tparams.setDim(1);
        for (size_t i = 0; i < parameters.dim; i++)
        {
            TemplateParameter tp = (*parameters)[i];
            tparams[0] = tp;

            for (size_t j = 0; j < parameters.dim; j++)
            {
                // Skip cases like: X(T : T)
                if (i == j)
                    continue;

                if (TemplateTypeParameter ttp = (*parameters)[j].isTemplateTypeParameter())
                {
                    if (reliesOnTident(ttp.specType, &tparams))
                        tp.dependent = true;
                }
                else if (TemplateAliasParameter tap = (*parameters)[j].isTemplateAliasParameter())
                {
                    if (reliesOnTident(tap.specType, &tparams) ||
                        reliesOnTident(isType(tap.specAlias), &tparams))
                    {
                        tp.dependent = true;
                    }
                }
            }
        }

        paramscope.pop();

        // Compute again
        onemember = null;
        if (members)
        {
            Dsymbol s;
            if (Dsymbol.oneMembers(members, &s, ident) && s)
            {
                onemember = s;
                s.parent = this;
            }
        }

        /* BUG: should check:
         *  o no virtual functions or non-static data members of classes
         */
    }

    /**********************************
     * Overload existing TemplateDeclaration 'this' with the new one 's'.
     * Return true if successful; i.e. no conflict.
     */
    override bool overloadInsert(Dsymbol s)
    {
        static if (LOG)
        {
            printf("TemplateDeclaration.overloadInsert('%s')\n", s.toChars());
        }
        FuncDeclaration fd = s.isFuncDeclaration();
        if (fd)
        {
            if (funcroot)
                return funcroot.overloadInsert(fd);
            funcroot = fd;
            return funcroot.overloadInsert(this);
        }

        TemplateDeclaration td = s.isTemplateDeclaration();
        if (!td)
            return false;

        TemplateDeclaration pthis = this;
        TemplateDeclaration* ptd;
        for (ptd = &pthis; *ptd; ptd = &(*ptd).overnext)
        {
        }

        td.overroot = this;
        *ptd = td;
        static if (LOG)
        {
            printf("\ttrue: no conflict\n");
        }
        return true;
    }

    override bool hasStaticCtorOrDtor()
    {
        return false; // don't scan uninstantiated templates
    }

    override const(char)* kind() const
    {
        return (onemember && onemember.isAggregateDeclaration()) ? onemember.kind() : "template";
    }

    override const(char)* toChars()
    {
        if (literal)
            return Dsymbol.toChars();

        OutBuffer buf;
        HdrGenState hgs;

        buf.writestring(ident.toChars());
        buf.writeByte('(');
        for (size_t i = 0; i < parameters.dim; i++)
        {
            TemplateParameter tp = (*parameters)[i];
            if (i)
                buf.writestring(", ");
            .toCBuffer(tp, &buf, &hgs);
        }
        buf.writeByte(')');

        if (onemember)
        {
            FuncDeclaration fd = onemember.isFuncDeclaration();
            if (fd && fd.type)
            {
                TypeFunction tf = cast(TypeFunction)fd.type;
                buf.writestring(parametersTypeToChars(tf.parameters, tf.varargs));
            }
        }

        if (constraint)
        {
            buf.writestring(" if (");
            .toCBuffer(constraint, &buf, &hgs);
            buf.writeByte(')');
        }
        return buf.extractString();
    }

    override Prot prot()
    {
        return protection;
    }

    /****************************
     * Check to see if constraint is satisfied.
     */
    bool evaluateConstraint(TemplateInstance ti, Scope* sc, Scope* paramscope, Objects* dedargs, FuncDeclaration fd)
    {
        /* Detect recursive attempts to instantiate this template declaration,
         * https://issues.dlang.org/show_bug.cgi?id=4072
         *  void foo(T)(T x) if (is(typeof(foo(x)))) { }
         *  static assert(!is(typeof(foo(7))));
         * Recursive attempts are regarded as a constraint failure.
         */
        /* There's a chicken-and-egg problem here. We don't know yet if this template
         * instantiation will be a local one (enclosing is set), and we won't know until
         * after selecting the correct template. Thus, function we're nesting inside
         * is not on the sc scope chain, and this can cause errors in FuncDeclaration.getLevel().
         * Workaround the problem by setting a flag to relax the checking on frame errors.
         */

        for (TemplatePrevious* p = previous; p; p = p.prev)
        {
            if (arrayObjectMatch(p.dedargs, dedargs))
            {
                //printf("recursive, no match p.sc=%p %p %s\n", p.sc, this, this.toChars());
                /* It must be a subscope of p.sc, other scope chains are not recursive
                 * instantiations.
                 */
                for (Scope* scx = sc; scx; scx = scx.enclosing)
                {
                    if (scx == p.sc)
                        return false;
                }
            }
            /* BUG: should also check for ref param differences
             */
        }

        TemplatePrevious pr;
        pr.prev = previous;
        pr.sc = paramscope;
        pr.dedargs = dedargs;
        previous = &pr; // add this to threaded list

        uint nerrors = global.errors;

        Scope* scx = paramscope.push(ti);
        scx.parent = ti;
        scx.tinst = null;
        scx.minst = null;

        assert(!ti.symtab);
        if (fd)
        {
            /* Declare all the function parameters as variables and add them to the scope
             * Making parameters is similar to FuncDeclaration.semantic3
             */
            TypeFunction tf = cast(TypeFunction)fd.type;
            assert(tf.ty == Tfunction);

            scx.parent = fd;

            Parameters* fparameters = tf.parameters;
            int fvarargs = tf.varargs;
            size_t nfparams = Parameter.dim(fparameters);
            for (size_t i = 0; i < nfparams; i++)
            {
                Parameter fparam = Parameter.getNth(fparameters, i);
                fparam.storageClass &= (STCin | STCout | STCref | STClazy | STCfinal | STC_TYPECTOR | STCnodtor);
                fparam.storageClass |= STCparameter;
                if (fvarargs == 2 && i + 1 == nfparams)
                    fparam.storageClass |= STCvariadic;
            }
            for (size_t i = 0; i < fparameters.dim; i++)
            {
                Parameter fparam = (*fparameters)[i];
                if (!fparam.ident)
                    continue;
                // don't add it, if it has no name
                auto v = new VarDeclaration(loc, fparam.type, fparam.ident, null);
                v.storage_class = fparam.storageClass;
                v.semantic(scx);
                if (!ti.symtab)
                    ti.symtab = new DsymbolTable();
                if (!scx.insert(v))
                    error("parameter %s.%s is already defined", toChars(), v.toChars());
                else
                    v.parent = fd;
            }
            if (isstatic)
                fd.storage_class |= STCstatic;
            fd.vthis = fd.declareThis(scx, fd.isThis());
        }

        Expression e = constraint.syntaxCopy();

        scx = scx.startCTFE();
        scx.flags |= SCOPEcondition | SCOPEconstraint;
        assert(ti.inst is null);
        ti.inst = ti; // temporary instantiation to enable genIdent()

        //printf("\tscx.parent = %s %s\n", scx.parent.kind(), scx.parent.toPrettyChars());
        e = e.semantic(scx);
        e = resolveProperties(scx, e);

        ti.inst = null;
        ti.symtab = null;
        scx = scx.endCTFE();

        scx = scx.pop();
        previous = pr.prev; // unlink from threaded list

        if (nerrors != global.errors) // if any errors from evaluating the constraint, no match
            return false;
        if (e.op == TOKerror)
            return false;

        e = e.ctfeInterpret();
        if (e.isBool(true))
        {
        }
        else if (e.isBool(false))
            return false;
        else
        {
            e.error("constraint %s is not constant or does not evaluate to a bool", e.toChars());
        }
        return true;
    }

    /***************************************
     * Given that ti is an instance of this TemplateDeclaration,
     * deduce the types of the parameters to this, and store
     * those deduced types in dedtypes[].
     * Input:
     *      flag    1: don't do semantic() because of dummy types
     *              2: don't change types in matchArg()
     * Output:
     *      dedtypes        deduced arguments
     * Return match level.
     */
    MATCH matchWithInstance(Scope* sc, TemplateInstance ti, Objects* dedtypes, Expressions* fargs, int flag)
    {
        enum LOGM = 0;
        static if (LOGM)
        {
            printf("\n+TemplateDeclaration.matchWithInstance(this = %s, ti = %s, flag = %d)\n", toChars(), ti.toChars(), flag);
        }
        version (none)
        {
            printf("dedtypes.dim = %d, parameters.dim = %d\n", dedtypes.dim, parameters.dim);
            if (ti.tiargs.dim)
                printf("ti.tiargs.dim = %d, [0] = %p\n", ti.tiargs.dim, (*ti.tiargs)[0]);
        }
        MATCH m;
        size_t dedtypes_dim = dedtypes.dim;

        dedtypes.zero();

        if (errors)
            return MATCHnomatch;

        size_t parameters_dim = parameters.dim;
        int variadic = isVariadic() !is null;

        // If more arguments than parameters, no match
        if (ti.tiargs.dim > parameters_dim && !variadic)
        {
            static if (LOGM)
            {
                printf(" no match: more arguments than parameters\n");
            }
            return MATCHnomatch;
        }

        assert(dedtypes_dim == parameters_dim);
        assert(dedtypes_dim >= ti.tiargs.dim || variadic);

        assert(_scope);

        // Set up scope for template parameters
        auto paramsym = new ScopeDsymbol();
        paramsym.parent = _scope.parent;
        Scope* paramscope = _scope.push(paramsym);
        paramscope.tinst = ti;
        paramscope.minst = sc.minst;
        paramscope.callsc = sc;
        paramscope.stc = 0;

        // Attempt type deduction
        m = MATCHexact;
        for (size_t i = 0; i < dedtypes_dim; i++)
        {
            MATCH m2;
            TemplateParameter tp = (*parameters)[i];
            Declaration sparam;

            //printf("\targument [%d]\n", i);
            static if (LOGM)
            {
                //printf("\targument [%d] is %s\n", i, oarg ? oarg.toChars() : "null");
                TemplateTypeParameter ttp = tp.isTemplateTypeParameter();
                if (ttp)
                    printf("\tparameter[%d] is %s : %s\n", i, tp.ident.toChars(), ttp.specType ? ttp.specType.toChars() : "");
            }

            m2 = tp.matchArg(ti.loc, paramscope, ti.tiargs, i, parameters, dedtypes, &sparam);
            //printf("\tm2 = %d\n", m2);
            if (m2 == MATCHnomatch)
            {
                version (none)
                {
                    printf("\tmatchArg() for parameter %i failed\n", i);
                }
                goto Lnomatch;
            }

            if (m2 < m)
                m = m2;

            if (!flag)
                sparam.semantic(paramscope);
            if (!paramscope.insert(sparam)) // TODO: This check can make more early
            {
                // in TemplateDeclaration.semantic, and
                // then we don't need to make sparam if flags == 0
                goto Lnomatch;
            }
        }

        if (!flag)
        {
            /* Any parameter left without a type gets the type of
             * its corresponding arg
             */
            for (size_t i = 0; i < dedtypes_dim; i++)
            {
                if (!(*dedtypes)[i])
                {
                    assert(i < ti.tiargs.dim);
                    (*dedtypes)[i] = cast(Type)(*ti.tiargs)[i];
                }
            }
        }

        if (m > MATCHnomatch && constraint && !flag)
        {
            if (ti.hasNestedArgs(ti.tiargs, this.isstatic)) // TODO: should gag error
                ti.parent = ti.enclosing;
            else
                ti.parent = this.parent;

            // Similar to doHeaderInstantiation
            FuncDeclaration fd = onemember ? onemember.isFuncDeclaration() : null;
            if (fd)
            {
                assert(fd.type.ty == Tfunction);
                TypeFunction tf = cast(TypeFunction)fd.type.syntaxCopy();

                fd = new FuncDeclaration(fd.loc, fd.endloc, fd.ident, fd.storage_class, tf);
                fd.parent = ti;
                fd.inferRetType = true;

                // Shouldn't run semantic on default arguments and return type.
                for (size_t i = 0; i < tf.parameters.dim; i++)
                    (*tf.parameters)[i].defaultArg = null;
                tf.next = null;

                // Resolve parameter types and 'auto ref's.
                tf.fargs = fargs;
                uint olderrors = global.startGagging();
                fd.type = tf.semantic(loc, paramscope);
                if (global.endGagging(olderrors))
                {
                    assert(fd.type.ty != Tfunction);
                    goto Lnomatch;
                }
                assert(fd.type.ty == Tfunction);
                fd.originalType = fd.type; // for mangling
            }

            // TODO: dedtypes => ti.tiargs ?
            if (!evaluateConstraint(ti, sc, paramscope, dedtypes, fd))
                goto Lnomatch;
        }

        static if (LOGM)
        {
            // Print out the results
            printf("--------------------------\n");
            printf("template %s\n", toChars());
            printf("instance %s\n", ti.toChars());
            if (m > MATCHnomatch)
            {
                for (size_t i = 0; i < dedtypes_dim; i++)
                {
                    TemplateParameter tp = (*parameters)[i];
                    RootObject oarg;
                    printf(" [%d]", i);
                    if (i < ti.tiargs.dim)
                        oarg = (*ti.tiargs)[i];
                    else
                        oarg = null;
                    tp.print(oarg, (*dedtypes)[i]);
                }
            }
            else
                goto Lnomatch;
        }
        static if (LOGM)
        {
            printf(" match = %d\n", m);
        }
        goto Lret;

    Lnomatch:
        static if (LOGM)
        {
            printf(" no match\n");
        }
        m = MATCHnomatch;

    Lret:
        paramscope.pop();
        static if (LOGM)
        {
            printf("-TemplateDeclaration.matchWithInstance(this = %p, ti = %p) = %d\n", this, ti, m);
        }
        return m;
    }

    /********************************************
     * Determine partial specialization order of 'this' vs td2.
     * Returns:
     *      match   this is at least as specialized as td2
     *      0       td2 is more specialized than this
     */
    MATCH leastAsSpecialized(Scope* sc, TemplateDeclaration td2, Expressions* fargs)
    {
        enum LOG_LEASTAS = 0;
        static if (LOG_LEASTAS)
        {
            printf("%s.leastAsSpecialized(%s)\n", toChars(), td2.toChars());
        }

        /* This works by taking the template parameters to this template
         * declaration and feeding them to td2 as if it were a template
         * instance.
         * If it works, then this template is at least as specialized
         * as td2.
         */

        // Set type arguments to dummy template instance to be types
        // generated from the parameters to this template declaration
        auto tiargs = new Objects();
        tiargs.reserve(parameters.dim);
        for (size_t i = 0; i < parameters.dim; i++)
        {
            TemplateParameter tp = (*parameters)[i];
            if (tp.dependent)
                break;
            RootObject p = cast(RootObject)tp.dummyArg();
            if (!p)
                break;

            tiargs.push(p);
        }
        scope TemplateInstance ti = new TemplateInstance(Loc(), ident, tiargs); // create dummy template instance

        // Temporary Array to hold deduced types
        Objects dedtypes;
        dedtypes.setDim(td2.parameters.dim);

        // Attempt a type deduction
        MATCH m = td2.matchWithInstance(sc, ti, &dedtypes, fargs, 1);
        if (m > MATCHnomatch)
        {
            /* A non-variadic template is more specialized than a
             * variadic one.
             */
            TemplateTupleParameter tp = isVariadic();
            if (tp && !tp.dependent && !td2.isVariadic())
                goto L1;

            static if (LOG_LEASTAS)
            {
                printf("  matches %d, so is least as specialized\n", m);
            }
            return m;
        }
    L1:
        static if (LOG_LEASTAS)
        {
            printf("  doesn't match, so is not as specialized\n");
        }
        return MATCHnomatch;
    }

    /*************************************************
     * Match function arguments against a specific template function.
     * Input:
     *      ti
     *      sc              instantiation scope
     *      fd
     *      tthis           'this' argument if !NULL
     *      fargs           arguments to function
     * Output:
     *      fd              Partially instantiated function declaration
     *      ti.tdtypes     Expression/Type deduced template arguments
     * Returns:
     *      match level
     *          bit 0-3     Match template parameters by inferred template arguments
     *          bit 4-7     Match template parameters by initial template arguments
     */
    MATCH deduceFunctionTemplateMatch(TemplateInstance ti, Scope* sc, ref FuncDeclaration fd, Type tthis, Expressions* fargs)
    {
        size_t nfparams;
        size_t nfargs;
        size_t ntargs; // array size of tiargs
        size_t fptupindex = IDX_NOTFOUND;
        MATCH match = MATCHexact;
        MATCH matchTiargs = MATCHexact;
        Parameters* fparameters; // function parameter list
        int fvarargs; // function varargs
        uint wildmatch = 0;
        size_t inferStart = 0;

        Loc instLoc = ti.loc;
        Objects* tiargs = ti.tiargs;
        auto dedargs = new Objects();
        Objects* dedtypes = &ti.tdtypes; // for T:T*, the dedargs is the T*, dedtypes is the T

        version (none)
        {
            printf("\nTemplateDeclaration.deduceFunctionTemplateMatch() %s\n", toChars());
            for (size_t i = 0; i < (fargs ? fargs.dim : 0); i++)
            {
                Expression e = (*fargs)[i];
                printf("\tfarg[%d] is %s, type is %s\n", i, e.toChars(), e.type.toChars());
            }
            printf("fd = %s\n", fd.toChars());
            printf("fd.type = %s\n", fd.type.toChars());
            if (tthis)
                printf("tthis = %s\n", tthis.toChars());
        }

        assert(_scope);

        dedargs.setDim(parameters.dim);
        dedargs.zero();

        dedtypes.setDim(parameters.dim);
        dedtypes.zero();

        if (errors || fd.errors)
            return MATCHnomatch;

        // Set up scope for parameters
        auto paramsym = new ScopeDsymbol();
        paramsym.parent = _scope.parent; // should use hasnestedArgs and enclosing?
        Scope* paramscope = _scope.push(paramsym);
        paramscope.tinst = ti;
        paramscope.minst = sc.minst;
        paramscope.callsc = sc;
        paramscope.stc = 0;

        TemplateTupleParameter tp = isVariadic();
        Tuple declaredTuple = null;

        version (none)
        {
            for (size_t i = 0; i < dedargs.dim; i++)
            {
                printf("\tdedarg[%d] = ", i);
                RootObject oarg = (*dedargs)[i];
                if (oarg)
                    printf("%s", oarg.toChars());
                printf("\n");
            }
        }

        ntargs = 0;
        if (tiargs)
        {
            // Set initial template arguments
            ntargs = tiargs.dim;
            size_t n = parameters.dim;
            if (tp)
                n--;
            if (ntargs > n)
            {
                if (!tp)
                    goto Lnomatch;

                /* The extra initial template arguments
                 * now form the tuple argument.
                 */
                auto t = new Tuple();
                assert(parameters.dim);
                (*dedargs)[parameters.dim - 1] = t;

                t.objects.setDim(ntargs - n);
                for (size_t i = 0; i < t.objects.dim; i++)
                {
                    t.objects[i] = (*tiargs)[n + i];
                }
                declareParameter(paramscope, tp, t);
                declaredTuple = t;
            }
            else
                n = ntargs;

            memcpy(dedargs.tdata(), tiargs.tdata(), n * (*dedargs.tdata()).sizeof);

            for (size_t i = 0; i < n; i++)
            {
                assert(i < parameters.dim);
                Declaration sparam = null;
                MATCH m = (*parameters)[i].matchArg(instLoc, paramscope, dedargs, i, parameters, dedtypes, &sparam);
                //printf("\tdeduceType m = %d\n", m);
                if (m <= MATCHnomatch)
                    goto Lnomatch;
                if (m < matchTiargs)
                    matchTiargs = m;

                sparam.semantic(paramscope);
                if (!paramscope.insert(sparam))
                    goto Lnomatch;
            }
            if (n < parameters.dim && !declaredTuple)
            {
                inferStart = n;
            }
            else
                inferStart = parameters.dim;
            //printf("tiargs matchTiargs = %d\n", matchTiargs);
        }
        version (none)
        {
            for (size_t i = 0; i < dedargs.dim; i++)
            {
                printf("\tdedarg[%d] = ", i);
                RootObject oarg = (*dedargs)[i];
                if (oarg)
                    printf("%s", oarg.toChars());
                printf("\n");
            }
        }

        fparameters = fd.getParameters(&fvarargs);
        nfparams = Parameter.dim(fparameters); // number of function parameters
        nfargs = fargs ? fargs.dim : 0; // number of function arguments

        /* Check for match of function arguments with variadic template
         * parameter, such as:
         *
         * void foo(T, A...)(T t, A a);
         * void main() { foo(1,2,3); }
         */
        if (tp) // if variadic
        {
            // TemplateTupleParameter always makes most lesser matching.
            matchTiargs = MATCHconvert;

            if (nfparams == 0 && nfargs != 0) // if no function parameters
            {
                if (!declaredTuple)
                {
                    auto t = new Tuple();
                    //printf("t = %p\n", t);
                    (*dedargs)[parameters.dim - 1] = t;
                    declareParameter(paramscope, tp, t);
                    declaredTuple = t;
                }
            }
            else
            {
                /* Figure out which of the function parameters matches
                 * the tuple template parameter. Do this by matching
                 * type identifiers.
                 * Set the index of this function parameter to fptupindex.
                 */
                for (fptupindex = 0; fptupindex < nfparams; fptupindex++)
                {
                    Parameter fparam = (*fparameters)[fptupindex];
                    if (fparam.type.ty != Tident)
                        continue;
                    TypeIdentifier tid = cast(TypeIdentifier)fparam.type;
                    if (!tp.ident.equals(tid.ident) || tid.idents.dim)
                        continue;

                    if (fvarargs) // variadic function doesn't
                        goto Lnomatch; // go with variadic template

                    goto L1;
                }
                fptupindex = IDX_NOTFOUND;
            L1:
            }
        }

        if (toParent().isModule() || (_scope.stc & STCstatic))
            tthis = null;
        if (tthis)
        {
            bool hasttp = false;

            // Match 'tthis' to any TemplateThisParameter's
            for (size_t i = 0; i < parameters.dim; i++)
            {
                TemplateThisParameter ttp = (*parameters)[i].isTemplateThisParameter();
                if (ttp)
                {
                    hasttp = true;

                    Type t = new TypeIdentifier(Loc(), ttp.ident);
                    MATCH m = deduceType(tthis, paramscope, t, parameters, dedtypes);
                    if (m <= MATCHnomatch)
                        goto Lnomatch;
                    if (m < match)
                        match = m; // pick worst match
                }
            }

            // Match attributes of tthis against attributes of fd
            if (fd.type && !fd.isCtorDeclaration())
            {
                StorageClass stc = _scope.stc | fd.storage_class2;
                // Propagate parent storage class, https://issues.dlang.org/show_bug.cgi?id=5504
                Dsymbol p = parent;
                while (p.isTemplateDeclaration() || p.isTemplateInstance())
                    p = p.parent;
                AggregateDeclaration ad = p.isAggregateDeclaration();
                if (ad)
                    stc |= ad.storage_class;

                ubyte mod = fd.type.mod;
                if (stc & STCimmutable)
                    mod = MODimmutable;
                else
                {
                    if (stc & (STCshared | STCsynchronized))
                        mod |= MODshared;
                    if (stc & STCconst)
                        mod |= MODconst;
                    if (stc & STCwild)
                        mod |= MODwild;
                }

                ubyte thismod = tthis.mod;
                if (hasttp)
                    mod = MODmerge(thismod, mod);
                MATCH m = MODmethodConv(thismod, mod);
                if (m <= MATCHnomatch)
                    goto Lnomatch;
                if (m < match)
                    match = m;
            }
        }

        // Loop through the function parameters
        {
            //printf("%s\n\tnfargs = %d, nfparams = %d, tuple_dim = %d\n", toChars(), nfargs, nfparams, declaredTuple ? declaredTuple.objects.dim : 0);
            //printf("\ttp = %p, fptupindex = %d, found = %d, declaredTuple = %s\n", tp, fptupindex, fptupindex != IDX_NOTFOUND, declaredTuple ? declaredTuple.toChars() : NULL);
            size_t argi = 0;
            size_t nfargs2 = nfargs; // nfargs + supplied defaultArgs
            for (size_t parami = 0; parami < nfparams; parami++)
            {
                Parameter fparam = Parameter.getNth(fparameters, parami);

                // Apply function parameter storage classes to parameter types
                Type prmtype = fparam.type.addStorageClass(fparam.storageClass);

                Expression farg;

                /* See function parameters which wound up
                 * as part of a template tuple parameter.
                 */
                if (fptupindex != IDX_NOTFOUND && parami == fptupindex)
                {
                    assert(prmtype.ty == Tident);
                    TypeIdentifier tid = cast(TypeIdentifier)prmtype;
                    if (!declaredTuple)
                    {
                        /* The types of the function arguments
                         * now form the tuple argument.
                         */
                        declaredTuple = new Tuple();
                        (*dedargs)[parameters.dim - 1] = declaredTuple;

                        /* Count function parameters following a tuple parameter.
                         * void foo(U, T...)(int y, T, U, int) {}  // rem == 2 (U, int)
                         */
                        size_t rem = 0;
                        for (size_t j = parami + 1; j < nfparams; j++)
                        {
                            Parameter p = Parameter.getNth(fparameters, j);
                            if (!reliesOnTident(p.type, parameters, inferStart))
                            {
                                Type pt = p.type.syntaxCopy().semantic(fd.loc, paramscope);
                                rem += pt.ty == Ttuple ? (cast(TypeTuple)pt).arguments.dim : 1;
                            }
                            else
                            {
                                ++rem;
                            }
                        }

                        if (nfargs2 - argi < rem)
                            goto Lnomatch;
                        declaredTuple.objects.setDim(nfargs2 - argi - rem);
                        for (size_t i = 0; i < declaredTuple.objects.dim; i++)
                        {
                            farg = (*fargs)[argi + i];

                            // Check invalid arguments to detect errors early.
                            if (farg.op == TOKerror || farg.type.ty == Terror)
                                goto Lnomatch;

                            if (!(fparam.storageClass & STClazy) && farg.type.ty == Tvoid)
                                goto Lnomatch;

                            Type tt;
                            MATCH m;
                            if (ubyte wm = deduceWildHelper(farg.type, &tt, tid))
                            {
                                wildmatch |= wm;
                                m = MATCHconst;
                            }
                            else
                            {
                                m = deduceTypeHelper(farg.type, &tt, tid);
                            }
                            if (m <= MATCHnomatch)
                                goto Lnomatch;
                            if (m < match)
                                match = m;

                            /* Remove top const for dynamic array types and pointer types
                             */
                            if ((tt.ty == Tarray || tt.ty == Tpointer) && !tt.isMutable() && (!(fparam.storageClass & STCref) || (fparam.storageClass & STCauto) && !farg.isLvalue()))
                            {
                                tt = tt.mutableOf();
                            }
                            declaredTuple.objects[i] = tt;
                        }
                        declareParameter(paramscope, tp, declaredTuple);
                    }
                    else
                    {
                        // https://issues.dlang.org/show_bug.cgi?id=6810
                        // If declared tuple is not a type tuple,
                        // it cannot be function parameter types.
                        for (size_t i = 0; i < declaredTuple.objects.dim; i++)
                        {
                            if (!isType(declaredTuple.objects[i]))
                                goto Lnomatch;
                        }
                    }
                    assert(declaredTuple);
                    argi += declaredTuple.objects.dim;
                    continue;
                }

                // If parameter type doesn't depend on inferred template parameters,
                // semantic it to get actual type.
                if (!reliesOnTident(prmtype, parameters, inferStart))
                {
                    // should copy prmtype to avoid affecting semantic result
                    prmtype = prmtype.syntaxCopy().semantic(fd.loc, paramscope);

                    if (prmtype.ty == Ttuple)
                    {
                        TypeTuple tt = cast(TypeTuple)prmtype;
                        size_t tt_dim = tt.arguments.dim;
                        for (size_t j = 0; j < tt_dim; j++, ++argi)
                        {
                            Parameter p = (*tt.arguments)[j];
                            if (j == tt_dim - 1 && fvarargs == 2 && parami + 1 == nfparams && argi < nfargs)
                            {
                                prmtype = p.type;
                                goto Lvarargs;
                            }
                            if (argi >= nfargs)
                            {
                                if (p.defaultArg)
                                    continue;
                                goto Lnomatch;
                            }
                            farg = (*fargs)[argi];
                            if (!farg.implicitConvTo(p.type))
                                goto Lnomatch;
                        }
                        continue;
                    }
                }

                if (argi >= nfargs) // if not enough arguments
                {
                    if (!fparam.defaultArg)
                        goto Lvarargs;

                    /* https://issues.dlang.org/show_bug.cgi?id=2803
                     * Before the starting of type deduction from the function
                     * default arguments, set the already deduced parameters into paramscope.
                     * It's necessary to avoid breaking existing acceptable code. Cases:
                     *
                     * 1. Already deduced template parameters can appear in fparam.defaultArg:
                     *  auto foo(A, B)(A a, B b = A.stringof);
                     *  foo(1);
                     *  // at fparam == 'B b = A.string', A is equivalent with the deduced type 'int'
                     *
                     * 2. If prmtype depends on default-specified template parameter, the
                     * default type should be preferred.
                     *  auto foo(N = size_t, R)(R r, N start = 0)
                     *  foo([1,2,3]);
                     *  // at fparam `N start = 0`, N should be 'size_t' before
                     *  // the deduction result from fparam.defaultArg.
                     */
                    if (argi == nfargs)
                    {
                        for (size_t i = 0; i < dedtypes.dim; i++)
                        {
                            Type at = isType((*dedtypes)[i]);
                            if (at && at.ty == Tnone)
                            {
                                TypeDeduced xt = cast(TypeDeduced)at;
                                (*dedtypes)[i] = xt.tded; // 'unbox'
                            }
                        }
                        for (size_t i = ntargs; i < dedargs.dim; i++)
                        {
                            TemplateParameter tparam = (*parameters)[i];

                            RootObject oarg = (*dedargs)[i];
                            RootObject oded = (*dedtypes)[i];
                            if (!oarg)
                            {
                                if (oded)
                                {
                                    if (tparam.specialization() || !tparam.isTemplateTypeParameter())
                                    {
                                        /* The specialization can work as long as afterwards
                                         * the oded == oarg
                                         */
                                        (*dedargs)[i] = oded;
                                        MATCH m2 = tparam.matchArg(instLoc, paramscope, dedargs, i, parameters, dedtypes, null);
                                        //printf("m2 = %d\n", m2);
                                        if (m2 <= MATCHnomatch)
                                            goto Lnomatch;
                                        if (m2 < matchTiargs)
                                            matchTiargs = m2; // pick worst match
                                        if (!(*dedtypes)[i].equals(oded))
                                            error("specialization not allowed for deduced parameter %s", tparam.ident.toChars());
                                    }
                                    else
                                    {
                                        if (MATCHconvert < matchTiargs)
                                            matchTiargs = MATCHconvert;
                                    }
                                    (*dedargs)[i] = declareParameter(paramscope, tparam, oded);
                                }
                                else
                                {
                                    oded = tparam.defaultArg(instLoc, paramscope);
                                    if (oded)
                                        (*dedargs)[i] = declareParameter(paramscope, tparam, oded);
                                }
                            }
                        }
                    }
                    nfargs2 = argi + 1;

                    /* If prmtype does not depend on any template parameters:
                     *
                     *  auto foo(T)(T v, double x = 0);
                     *  foo("str");
                     *  // at fparam == 'double x = 0'
                     *
                     * or, if all template parameters in the prmtype are already deduced:
                     *
                     *  auto foo(R)(R range, ElementType!R sum = 0);
                     *  foo([1,2,3]);
                     *  // at fparam == 'ElementType!R sum = 0'
                     *
                     * Deducing prmtype from fparam.defaultArg is not necessary.
                     */
                    if (prmtype.deco || prmtype.syntaxCopy().trySemantic(loc, paramscope))
                    {
                        ++argi;
                        continue;
                    }

                    // Deduce prmtype from the defaultArg.
                    farg = fparam.defaultArg.syntaxCopy();
                    farg = farg.semantic(paramscope);
                    farg = resolveProperties(paramscope, farg);
                }
                else
                {
                    farg = (*fargs)[argi];
                }
                {
                    // Check invalid arguments to detect errors early.
                    if (farg.op == TOKerror || farg.type.ty == Terror)
                        goto Lnomatch;

                    Type att = null;
                Lretry:
                    version (none)
                    {
                        printf("\tfarg.type   = %s\n", farg.type.toChars());
                        printf("\tfparam.type = %s\n", prmtype.toChars());
                    }
                    Type argtype = farg.type;

                    if (!(fparam.storageClass & STClazy) && argtype.ty == Tvoid && farg.op != TOKfunction)
                        goto Lnomatch;

                    // https://issues.dlang.org/show_bug.cgi?id=12876
                    // Optimize argument to allow CT-known length matching
                    farg = farg.optimize(WANTvalue, (fparam.storageClass & (STCref | STCout)) != 0);
                    //printf("farg = %s %s\n", farg.type.toChars(), farg.toChars());

                    RootObject oarg = farg;
                    if ((fparam.storageClass & STCref) && (!(fparam.storageClass & STCauto) || farg.isLvalue()))
                    {
                        /* Allow expressions that have CT-known boundaries and type [] to match with [dim]
                         */
                        Type taai;
                        if (argtype.ty == Tarray && (prmtype.ty == Tsarray || prmtype.ty == Taarray && (taai = (cast(TypeAArray)prmtype).index).ty == Tident && (cast(TypeIdentifier)taai).idents.dim == 0))
                        {
                            if (farg.op == TOKstring)
                            {
                                StringExp se = cast(StringExp)farg;
                                argtype = se.type.nextOf().sarrayOf(se.len);
                            }
                            else if (farg.op == TOKarrayliteral)
                            {
                                ArrayLiteralExp ae = cast(ArrayLiteralExp)farg;
                                argtype = ae.type.nextOf().sarrayOf(ae.elements.dim);
                            }
                            else if (farg.op == TOKslice)
                            {
                                SliceExp se = cast(SliceExp)farg;
                                if (Type tsa = toStaticArrayType(se))
                                    argtype = tsa;
                            }
                        }

                        oarg = argtype;
                    }
                    else if ((fparam.storageClass & STCout) == 0 && (argtype.ty == Tarray || argtype.ty == Tpointer) && templateParameterLookup(prmtype, parameters) != IDX_NOTFOUND && (cast(TypeIdentifier)prmtype).idents.dim == 0)
                    {
                        /* The farg passing to the prmtype always make a copy. Therefore,
                         * we can shrink the set of the deduced type arguments for prmtype
                         * by adjusting top-qualifier of the argtype.
                         *
                         *  prmtype         argtype     ta
                         *  T            <- const(E)[]  const(E)[]
                         *  T            <- const(E[])  const(E)[]
                         *  qualifier(T) <- const(E)[]  const(E[])
                         *  qualifier(T) <- const(E[])  const(E[])
                         */
                        Type ta = argtype.castMod(prmtype.mod ? argtype.nextOf().mod : 0);
                        if (ta != argtype)
                        {
                            Expression ea = farg.copy();
                            ea.type = ta;
                            oarg = ea;
                        }
                    }

                    if (fvarargs == 2 && parami + 1 == nfparams && argi + 1 < nfargs)
                        goto Lvarargs;

                    uint wm = 0;
                    MATCH m = deduceType(oarg, paramscope, prmtype, parameters, dedtypes, &wm, inferStart);
                    //printf("\tL%d deduceType m = %d, wm = x%x, wildmatch = x%x\n", __LINE__, m, wm, wildmatch);
                    wildmatch |= wm;

                    /* If no match, see if the argument can be matched by using
                     * implicit conversions.
                     */
                    if (m == MATCHnomatch && prmtype.deco)
                        m = farg.implicitConvTo(prmtype);

                    if (m == MATCHnomatch)
                    {
                        AggregateDeclaration ad = isAggregate(farg.type);
                        if (ad && ad.aliasthis && argtype != att)
                        {
                            if (!att && argtype.checkAliasThisRec())   // https://issues.dlang.org/show_bug.cgi?id=12537
                                att = argtype;
                            /* If a semantic error occurs while doing alias this,
                             * eg purity(https://issues.dlang.org/show_bug.cgi?id=7295),
                             * just regard it as not a match.
                             */
                            if (auto e = resolveAliasThis(sc, farg, true))
                            {
                                farg = e;
                                goto Lretry;
                            }
                        }
                    }

                    if (m > MATCHnomatch && (fparam.storageClass & (STCref | STCauto)) == STCref)
                    {
                        if (!farg.isLvalue())
                        {
                            if ((farg.op == TOKstring || farg.op == TOKslice) && (prmtype.ty == Tsarray || prmtype.ty == Taarray))
                            {
                                // Allow conversion from T[lwr .. upr] to ref T[upr-lwr]
                            }
                            else
                                goto Lnomatch;
                        }
                    }
                    if (m > MATCHnomatch && (fparam.storageClass & STCout))
                    {
                        if (!farg.isLvalue())
                            goto Lnomatch;
                        if (!farg.type.isMutable()) // https://issues.dlang.org/show_bug.cgi?id=11916
                            goto Lnomatch;
                    }
                    if (m == MATCHnomatch && (fparam.storageClass & STClazy) && prmtype.ty == Tvoid && farg.type.ty != Tvoid)
                        m = MATCHconvert;
                    if (m != MATCHnomatch)
                    {
                        if (m < match)
                            match = m; // pick worst match
                        argi++;
                        continue;
                    }
                }

            Lvarargs:
                /* The following code for variadic arguments closely
                 * matches TypeFunction.callMatch()
                 */
                if (!(fvarargs == 2 && parami + 1 == nfparams))
                    goto Lnomatch;

                /* Check for match with function parameter T...
                 */
                Type tb = prmtype.toBasetype();
                switch (tb.ty)
                {
                    // 6764 fix - TypeAArray may be TypeSArray have not yet run semantic().
                case Tsarray:
                case Taarray:
                    {
                        // Perhaps we can do better with this, see TypeFunction.callMatch()
                        if (tb.ty == Tsarray)
                        {
                            TypeSArray tsa = cast(TypeSArray)tb;
                            dinteger_t sz = tsa.dim.toInteger();
                            if (sz != nfargs - argi)
                                goto Lnomatch;
                        }
                        else if (tb.ty == Taarray)
                        {
                            TypeAArray taa = cast(TypeAArray)tb;
                            Expression dim = new IntegerExp(instLoc, nfargs - argi, Type.tsize_t);

                            size_t i = templateParameterLookup(taa.index, parameters);
                            if (i == IDX_NOTFOUND)
                            {
                                Expression e;
                                Type t;
                                Dsymbol s;
                                Scope *sco;

                                uint errors = global.startGagging();
                                /* ref: https://issues.dlang.org/show_bug.cgi?id=11118
                                 * The parameter isn't part of the template
                                 * ones, let's try to find it in the
                                 * instantiation scope 'sc' and the one
                                 * belonging to the template itself. */
                                sco = sc;
                                taa.index.resolve(instLoc, sco, &e, &t, &s);
                                if (!e)
                                {
                                    sco = paramscope;
                                    taa.index.resolve(instLoc, sco, &e, &t, &s);
                                }
                                global.endGagging(errors);

                                if (!e)
                                {
                                    goto Lnomatch;
                                }

                                e = e.ctfeInterpret();
                                e = e.implicitCastTo(sco, Type.tsize_t);
                                e = e.optimize(WANTvalue);
                                if (!dim.equals(e))
                                    goto Lnomatch;
                            }
                            else
                            {
                                // This code matches code in TypeInstance.deduceType()
                                TemplateParameter tprm = (*parameters)[i];
                                TemplateValueParameter tvp = tprm.isTemplateValueParameter();
                                if (!tvp)
                                    goto Lnomatch;
                                Expression e = cast(Expression)(*dedtypes)[i];
                                if (e)
                                {
                                    if (!dim.equals(e))
                                        goto Lnomatch;
                                }
                                else
                                {
                                    Type vt = tvp.valType.semantic(Loc(), sc);
                                    MATCH m = dim.implicitConvTo(vt);
                                    if (m <= MATCHnomatch)
                                        goto Lnomatch;
                                    (*dedtypes)[i] = dim;
                                }
                            }
                        }
                        goto case Tarray;
                    }
                case Tarray:
                    {
                        TypeArray ta = cast(TypeArray)tb;
                        Type tret = fparam.isLazyArray();
                        for (; argi < nfargs; argi++)
                        {
                            Expression arg = (*fargs)[argi];
                            assert(arg);

                            MATCH m;
                            /* If lazy array of delegates,
                             * convert arg(s) to delegate(s)
                             */
                            if (tret)
                            {
                                if (ta.next.equals(arg.type))
                                {
                                    m = MATCHexact;
                                }
                                else
                                {
                                    m = arg.implicitConvTo(tret);
                                    if (m == MATCHnomatch)
                                    {
                                        if (tret.toBasetype().ty == Tvoid)
                                            m = MATCHconvert;
                                    }
                                }
                            }
                            else
                            {
                                uint wm = 0;
                                m = deduceType(arg, paramscope, ta.next, parameters, dedtypes, &wm, inferStart);
                                wildmatch |= wm;
                            }
                            if (m == MATCHnomatch)
                                goto Lnomatch;
                            if (m < match)
                                match = m;
                        }
                        goto Lmatch;
                    }
                case Tclass:
                case Tident:
                    goto Lmatch;

                default:
                    goto Lnomatch;
                }
                assert(0);
            }
            //printf(". argi = %d, nfargs = %d, nfargs2 = %d\n", argi, nfargs, nfargs2);
            if (argi != nfargs2 && !fvarargs)
                goto Lnomatch;
        }

    Lmatch:
        for (size_t i = 0; i < dedtypes.dim; i++)
        {
            Type at = isType((*dedtypes)[i]);
            if (at)
            {
                if (at.ty == Tnone)
                {
                    TypeDeduced xt = cast(TypeDeduced)at;
                    at = xt.tded; // 'unbox'
                }
                (*dedtypes)[i] = at.merge2();
            }
        }
        for (size_t i = ntargs; i < dedargs.dim; i++)
        {
            TemplateParameter tparam = (*parameters)[i];
            //printf("tparam[%d] = %s\n", i, tparam.ident.toChars());

            /* For T:T*, the dedargs is the T*, dedtypes is the T
             * But for function templates, we really need them to match
             */
            RootObject oarg = (*dedargs)[i];
            RootObject oded = (*dedtypes)[i];
            //printf("1dedargs[%d] = %p, dedtypes[%d] = %p\n", i, oarg, i, oded);
            //if (oarg) printf("oarg: %s\n", oarg.toChars());
            //if (oded) printf("oded: %s\n", oded.toChars());
            if (!oarg)
            {
                if (oded)
                {
                    if (tparam.specialization() || !tparam.isTemplateTypeParameter())
                    {
                        /* The specialization can work as long as afterwards
                         * the oded == oarg
                         */
                        (*dedargs)[i] = oded;
                        MATCH m2 = tparam.matchArg(instLoc, paramscope, dedargs, i, parameters, dedtypes, null);
                        //printf("m2 = %d\n", m2);
                        if (m2 <= MATCHnomatch)
                            goto Lnomatch;
                        if (m2 < matchTiargs)
                            matchTiargs = m2; // pick worst match
                        if (!(*dedtypes)[i].equals(oded))
                            error("specialization not allowed for deduced parameter %s", tparam.ident.toChars());
                    }
                    else
                    {
                        // Discussion: https://issues.dlang.org/show_bug.cgi?id=16484
                        if (MATCHconvert < matchTiargs)
                            matchTiargs = MATCHconvert;
                    }
                }
                else
                {
                    oded = tparam.defaultArg(instLoc, paramscope);
                    if (!oded)
                    {
                        // if tuple parameter and
                        // tuple parameter was not in function parameter list and
                        // we're one or more arguments short (i.e. no tuple argument)
                        if (tparam == tp &&
                            fptupindex == IDX_NOTFOUND &&
                            ntargs <= dedargs.dim - 1)
                        {
                            // make tuple argument an empty tuple
                            oded = cast(RootObject)new Tuple();
                        }
                        else
                            goto Lnomatch;
                    }
                    if (isError(oded))
                        goto Lerror;
                    ntargs++;

                    /* At the template parameter T, the picked default template argument
                     * X!int should be matched to T in order to deduce dependent
                     * template parameter A.
                     *  auto foo(T : X!A = X!int, A...)() { ... }
                     *  foo();  // T <-- X!int, A <-- (int)
                     */
                    if (tparam.specialization())
                    {
                        (*dedargs)[i] = oded;
                        MATCH m2 = tparam.matchArg(instLoc, paramscope, dedargs, i, parameters, dedtypes, null);
                        //printf("m2 = %d\n", m2);
                        if (m2 <= MATCHnomatch)
                            goto Lnomatch;
                        if (m2 < matchTiargs)
                            matchTiargs = m2; // pick worst match
                        if (!(*dedtypes)[i].equals(oded))
                            error("specialization not allowed for deduced parameter %s", tparam.ident.toChars());
                    }
                }
                oded = declareParameter(paramscope, tparam, oded);
                (*dedargs)[i] = oded;
            }
        }

        /* https://issues.dlang.org/show_bug.cgi?id=7469
         * As same as the code for 7469 in findBestMatch,
         * expand a Tuple in dedargs to normalize template arguments.
         */
        if (auto d = dedargs.dim)
        {
            if (auto va = isTuple((*dedargs)[d - 1]))
            {
                dedargs.setDim(d - 1);
                dedargs.insert(d - 1, &va.objects);
            }
        }
        ti.tiargs = dedargs; // update to the normalized template arguments.

        // Partially instantiate function for constraint and fd.leastAsSpecialized()
        {
            assert(paramsym);
            Scope* sc2 = _scope;
            sc2 = sc2.push(paramsym);
            sc2 = sc2.push(ti);
            sc2.parent = ti;
            sc2.tinst = ti;
            sc2.minst = sc.minst;

            fd = doHeaderInstantiation(ti, sc2, fd, tthis, fargs);

            sc2 = sc2.pop();
            sc2 = sc2.pop();

            if (!fd)
                goto Lnomatch;
        }

        if (constraint)
        {
            if (!evaluateConstraint(ti, sc, paramscope, dedargs, fd))
                goto Lnomatch;
        }

        version (none)
        {
            for (size_t i = 0; i < dedargs.dim; i++)
            {
                RootObject o = (*dedargs)[i];
                printf("\tdedargs[%d] = %d, %s\n", i, o.dyncast(), o.toChars());
            }
        }

        paramscope.pop();
        //printf("\tmatch %d\n", match);
        return cast(MATCH)(match | (matchTiargs << 4));

    Lnomatch:
        paramscope.pop();
        //printf("\tnomatch\n");
        return MATCHnomatch;

    Lerror:
        // todo: for the future improvement
        paramscope.pop();
        //printf("\terror\n");
        return MATCHnomatch;
    }

    /**************************************************
     * Declare template parameter tp with value o, and install it in the scope sc.
     */
    RootObject declareParameter(Scope* sc, TemplateParameter tp, RootObject o)
    {
        //printf("TemplateDeclaration.declareParameter('%s', o = %p)\n", tp.ident.toChars(), o);
        Type ta = isType(o);
        Expression ea = isExpression(o);
        Dsymbol sa = isDsymbol(o);
        Tuple va = isTuple(o);

        Declaration d;
        VarDeclaration v = null;

        if (ea && ea.op == TOKtype)
            ta = ea.type;
        else if (ea && ea.op == TOKscope)
            sa = (cast(ScopeExp)ea).sds;
        else if (ea && (ea.op == TOKthis || ea.op == TOKsuper))
            sa = (cast(ThisExp)ea).var;
        else if (ea && ea.op == TOKfunction)
        {
            if ((cast(FuncExp)ea).td)
                sa = (cast(FuncExp)ea).td;
            else
                sa = (cast(FuncExp)ea).fd;
        }

        if (ta)
        {
            //printf("type %s\n", ta.toChars());
            d = new AliasDeclaration(Loc(), tp.ident, ta);
        }
        else if (sa)
        {
            //printf("Alias %s %s;\n", sa.ident.toChars(), tp.ident.toChars());
            d = new AliasDeclaration(Loc(), tp.ident, sa);
        }
        else if (ea)
        {
            // tdtypes.data[i] always matches ea here
            Initializer _init = new ExpInitializer(loc, ea);
            TemplateValueParameter tvp = tp.isTemplateValueParameter();
            Type t = tvp ? tvp.valType : null;
            v = new VarDeclaration(loc, t, tp.ident, _init);
            v.storage_class = STCmanifest | STCtemplateparameter;
            d = v;
        }
        else if (va)
        {
            //printf("\ttuple\n");
            d = new TupleDeclaration(loc, tp.ident, &va.objects);
        }
        else
        {
            debug
            {
                o.print();
            }
            assert(0);
        }
        d.storage_class |= STCtemplateparameter;

        if (ta)
        {
            Type t = ta;
            // consistent with Type.checkDeprecated()
            while (t.ty != Tenum)
            {
                if (!t.nextOf())
                    break;
                t = (cast(TypeNext)t).next;
            }
            if (Dsymbol s = t.toDsymbol(sc))
            {
                if (s.isDeprecated())
                    d.storage_class |= STCdeprecated;
            }
        }
        else if (sa)
        {
            if (sa.isDeprecated())
                d.storage_class |= STCdeprecated;
        }

        if (!sc.insert(d))
            error("declaration %s is already defined", tp.ident.toChars());
        d.semantic(sc);
        /* So the caller's o gets updated with the result of semantic() being run on o
         */
        if (v)
            o = v._init.toExpression();
        return o;
    }

    /*************************************************
     * Limited function template instantiation for using fd.leastAsSpecialized()
     */
    FuncDeclaration doHeaderInstantiation(TemplateInstance ti, Scope* sc2, FuncDeclaration fd, Type tthis, Expressions* fargs)
    {
        assert(fd);
        version (none)
        {
            printf("doHeaderInstantiation this = %s\n", toChars());
        }

        // function body and contracts are not need
        if (fd.isCtorDeclaration())
            fd = new CtorDeclaration(fd.loc, fd.endloc, fd.storage_class, fd.type.syntaxCopy());
        else
            fd = new FuncDeclaration(fd.loc, fd.endloc, fd.ident, fd.storage_class, fd.type.syntaxCopy());
        fd.parent = ti;

        assert(fd.type.ty == Tfunction);
        TypeFunction tf = cast(TypeFunction)fd.type;
        tf.fargs = fargs;

        if (tthis)
        {
            // Match 'tthis' to any TemplateThisParameter's
            bool hasttp = false;
            for (size_t i = 0; i < parameters.dim; i++)
            {
                TemplateParameter tp = (*parameters)[i];
                TemplateThisParameter ttp = tp.isTemplateThisParameter();
                if (ttp)
                    hasttp = true;
            }
            if (hasttp)
            {
                tf = cast(TypeFunction)tf.addSTC(ModToStc(tthis.mod));
                assert(!tf.deco);
            }
        }

        Scope* scx = sc2.push();

        // Shouldn't run semantic on default arguments and return type.
        for (size_t i = 0; i < tf.parameters.dim; i++)
            (*tf.parameters)[i].defaultArg = null;
        if (fd.isCtorDeclaration())
        {
            // For constructors, emitting return type is necessary for
            // isolateReturn() in functionResolve.
            scx.flags |= SCOPEctor;

            Dsymbol parent = toParent2();
            Type tret;
            AggregateDeclaration ad = parent.isAggregateDeclaration();
            if (!ad || parent.isUnionDeclaration())
            {
                tret = Type.tvoid;
            }
            else
            {
                tret = ad.handleType();
                assert(tret);
                tret = tret.addStorageClass(fd.storage_class | scx.stc);
                tret = tret.addMod(tf.mod);
            }
            tf.next = tret;
            if (ad && ad.isStructDeclaration())
                tf.isref = 1;
            //printf("tf = %s\n", tf.toChars());
        }
        else
            tf.next = null;
        fd.type = tf;
        fd.type = fd.type.addSTC(scx.stc);
        fd.type = fd.type.semantic(fd.loc, scx);
        scx = scx.pop();

        if (fd.type.ty != Tfunction)
            return null;

        fd.originalType = fd.type; // for mangling
        //printf("\t[%s] fd.type = %s, mod = %x, ", loc.toChars(), fd.type.toChars(), fd.type.mod);
        //printf("fd.needThis() = %d\n", fd.needThis());

        return fd;
    }

    debug (FindExistingInstance)
    {
        __gshared uint nFound, nNotFound, nAdded, nRemoved;

        shared static ~this()
        {
            printf("debug (FindExistingInstance) nFound %u, nNotFound: %u, nAdded: %u, nRemoved: %u\n",
                   nFound, nNotFound, nAdded, nRemoved);
        }
    }

    /****************************************************
     * Given a new instance tithis of this TemplateDeclaration,
     * see if there already exists an instance.
     * If so, return that existing instance.
     */
    TemplateInstance findExistingInstance(TemplateInstance tithis, Expressions* fargs)
    {
        //printf("findExistingInstance(%p)\n", tithis);
        tithis.fargs = fargs;
        auto tibox = TemplateInstanceBox(tithis);
        auto p = tibox in instances;
        debug (FindExistingInstance) ++(p ? nFound : nNotFound);
        //if (p) printf("\tfound %p\n", *p); else printf("\tnot found\n");
        return p ? *p : null;
    }

    /********************************************
     * Add instance ti to TemplateDeclaration's table of instances.
     * Return a handle we can use to later remove it if it fails instantiation.
     */
    TemplateInstance addInstance(TemplateInstance ti)
    {
        //printf("addInstance() %p %p\n", instances, ti);
        auto tibox = TemplateInstanceBox(ti);
        instances[tibox] = ti;
        debug (FindExistingInstance) ++nAdded;
        return ti;
    }

    /*******************************************
     * Remove TemplateInstance from table of instances.
     * Input:
     *      handle returned by addInstance()
     */
    void removeInstance(TemplateInstance ti)
    {
        //printf("removeInstance()\n");
        auto tibox = TemplateInstanceBox(ti);
        debug (FindExistingInstance) ++nRemoved;
        instances.remove(tibox);
    }

    override inout(TemplateDeclaration) isTemplateDeclaration() inout
    {
        return this;
    }

    /**
     * Check if the last template parameter is a tuple one,
     * and returns it if so, else returns `null`.
     *
     * Returns:
     *   The last template parameter if it's a `TemplateTupleParameter`
     */
    TemplateTupleParameter isVariadic()
    {
        size_t dim = parameters.dim;
        if (dim == 0)
            return null;
        return (*parameters)[dim - 1].isTemplateTupleParameter();
    }

    /***********************************
     * We can overload templates.
     */
    override bool isOverloadable()
    {
        return true;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

extern (C++) final class TypeDeduced : Type
{
    Type tded;
    Expressions argexps; // corresponding expressions
    Types tparams; // tparams[i].mod

    extern (D) this(Type tt, Expression e, Type tparam)
    {
        super(Tnone);
        tded = tt;
        argexps.push(e);
        tparams.push(tparam);
    }

    void update(Expression e, Type tparam)
    {
        argexps.push(e);
        tparams.push(tparam);
    }

    void update(Type tt, Expression e, Type tparam)
    {
        tded = tt;
        argexps.push(e);
        tparams.push(tparam);
    }

    MATCH matchAll(Type tt)
    {
        MATCH match = MATCHexact;
        for (size_t j = 0; j < argexps.dim; j++)
        {
            Expression e = argexps[j];
            assert(e);
            if (e == emptyArrayElement)
                continue;

            Type t = tt.addMod(tparams[j].mod).substWildTo(MODconst);

            MATCH m = e.implicitConvTo(t);
            if (match > m)
                match = m;
            if (match <= MATCHnomatch)
                break;
        }
        return match;
    }
}


/*************************************************
 * Given function arguments, figure out which template function
 * to expand, and return matching result.
 * Input:
 *      m               matching result
 *      dstart          the root of overloaded function templates
 *      loc             instantiation location
 *      sc              instantiation scope
 *      tiargs          initial list of template arguments
 *      tthis           if !NULL, the 'this' pointer argument
 *      fargs           arguments to function
 */
void functionResolve(Match* m, Dsymbol dstart, Loc loc, Scope* sc, Objects* tiargs, Type tthis, Expressions* fargs)
{
    version (none)
    {
        printf("functionResolve() dstart = %s\n", dstart.toChars());
        printf("    tiargs:\n");
        if (tiargs)
        {
            for (size_t i = 0; i < tiargs.dim; i++)
            {
                RootObject arg = (*tiargs)[i];
                printf("\t%s\n", arg.toChars());
            }
        }
        printf("    fargs:\n");
        for (size_t i = 0; i < (fargs ? fargs.dim : 0); i++)
        {
            Expression arg = (*fargs)[i];
            printf("\t%s %s\n", arg.type.toChars(), arg.toChars());
            //printf("\tty = %d\n", arg.type.ty);
        }
        //printf("stc = %llx\n", dstart.scope.stc);
        //printf("match:t/f = %d/%d\n", ta_last, m.last);
    }

    // results
    int property = 0;   // 0: unintialized
                        // 1: seen @property
                        // 2: not @property
    size_t ov_index = 0;
    TemplateDeclaration td_best;
    TemplateInstance ti_best;
    MATCH ta_last = m.last != MATCHnomatch ? MATCHexact : MATCHnomatch;
    Type tthis_best;

    int applyFunction(FuncDeclaration fd)
    {
        // skip duplicates
        if (fd == m.lastf)
            return 0;
        // explicitly specified tiargs never match to non template function
        if (tiargs && tiargs.dim > 0)
            return 0;

        if (fd.semanticRun == PASSinit && fd._scope)
        {
            Ungag ungag = fd.ungagSpeculative();
            fd.semantic(fd._scope);
        }
        if (fd.semanticRun == PASSinit)
        {
            .error(loc, "forward reference to template %s", fd.toChars());
            return 1;
        }
        //printf("fd = %s %s, fargs = %s\n", fd.toChars(), fd.type.toChars(), fargs.toChars());
        m.anyf = fd;
        auto tf = cast(TypeFunction)fd.type;

        int prop = tf.isproperty ? 1 : 2;
        if (property == 0)
            property = prop;
        else if (property != prop)
            error(fd.loc, "cannot overload both property and non-property functions");

        /* For constructors, qualifier check will be opposite direction.
         * Qualified constructor always makes qualified object, then will be checked
         * that it is implicitly convertible to tthis.
         */
        Type tthis_fd = fd.needThis() ? tthis : null;
        bool isCtorCall = tthis_fd && fd.isCtorDeclaration();
        if (isCtorCall)
        {
            //printf("%s tf.mod = x%x tthis_fd.mod = x%x %d\n", tf.toChars(),
            //        tf.mod, tthis_fd.mod, fd.isolateReturn());
            if (MODimplicitConv(tf.mod, tthis_fd.mod) ||
                tf.isWild() && tf.isShared() == tthis_fd.isShared() ||
                fd.isolateReturn())
            {
                /* && tf.isShared() == tthis_fd.isShared()*/
                // Uniquely constructed object can ignore shared qualifier.
                // TODO: Is this appropriate?
                tthis_fd = null;
            }
            else
                return 0;   // MATCHnomatch
        }
        MATCH mfa = tf.callMatch(tthis_fd, fargs);
        //printf("test1: mfa = %d\n", mfa);
        if (mfa > MATCHnomatch)
        {
            if (mfa > m.last) goto LfIsBetter;
            if (mfa < m.last) goto LlastIsBetter;

            /* See if one of the matches overrides the other.
             */
            assert(m.lastf);
            if (m.lastf.overrides(fd)) goto LlastIsBetter;
            if (fd.overrides(m.lastf)) goto LfIsBetter;

            /* Try to disambiguate using template-style partial ordering rules.
             * In essence, if f() and g() are ambiguous, if f() can call g(),
             * but g() cannot call f(), then pick f().
             * This is because f() is "more specialized."
             */
            {
                MATCH c1 = fd.leastAsSpecialized(m.lastf);
                MATCH c2 = m.lastf.leastAsSpecialized(fd);
                //printf("c1 = %d, c2 = %d\n", c1, c2);
                if (c1 > c2) goto LfIsBetter;
                if (c1 < c2) goto LlastIsBetter;
            }

            /* If the two functions are the same function, like:
             *    int foo(int);
             *    int foo(int x) { ... }
             * then pick the one with the body.
             */
            if (tf.equals(m.lastf.type) &&
                fd.storage_class == m.lastf.storage_class &&
                fd.parent == m.lastf.parent &&
                fd.protection == m.lastf.protection &&
                fd.linkage == m.lastf.linkage)
            {
                if (fd.fbody && !m.lastf.fbody) goto LfIsBetter;
                if (!fd.fbody && m.lastf.fbody) goto LlastIsBetter;
            }

            // https://issues.dlang.org/show_bug.cgi?id=14450
            // Prefer exact qualified constructor for the creating object type
            if (isCtorCall && tf.mod != m.lastf.type.mod)
            {
                if (tthis.mod == tf.mod) goto LfIsBetter;
                if (tthis.mod == m.lastf.type.mod) goto LlastIsBetter;
            }

            m.nextf = fd;
            m.count++;
            return 0;

        LlastIsBetter:
            return 0;

        LfIsBetter:
            td_best = null;
            ti_best = null;
            ta_last = MATCHexact;
            m.last = mfa;
            m.lastf = fd;
            tthis_best = tthis_fd;
            ov_index = 0;
            m.count = 1;
            return 0;
        }
        return 0;
    }

    int applyTemplate(TemplateDeclaration td)
    {
        //printf("applyTemplate()\n");
        // skip duplicates
        if (td == td_best)
            return 0;

        if (!sc)
            sc = td._scope; // workaround for Type.aliasthisOf

        if (td.semanticRun == PASSinit && td._scope)
        {
            // Try to fix forward reference. Ungag errors while doing so.
            Ungag ungag = td.ungagSpeculative();
            td.semantic(td._scope);
        }
        if (td.semanticRun == PASSinit)
        {
            .error(loc, "forward reference to template %s", td.toChars());
        Lerror:
            m.lastf = null;
            m.count = 0;
            m.last = MATCHnomatch;
            return 1;
        }
        //printf("td = %s\n", td.toChars());

        auto f = td.onemember ? td.onemember.isFuncDeclaration() : null;
        if (!f)
        {
            if (!tiargs)
                tiargs = new Objects();
            auto ti = new TemplateInstance(loc, td, tiargs);
            Objects dedtypes;
            dedtypes.setDim(td.parameters.dim);
            assert(td.semanticRun != PASSinit);
            MATCH mta = td.matchWithInstance(sc, ti, &dedtypes, fargs, 0);
            //printf("matchWithInstance = %d\n", mta);
            if (mta <= MATCHnomatch || mta < ta_last)   // no match or less match
                return 0;

            ti.semantic(sc, fargs);
            if (!ti.inst)               // if template failed to expand
                return 0;

            Dsymbol s = ti.inst.toAlias();
            FuncDeclaration fd;
            if (auto tdx = s.isTemplateDeclaration())
            {
                Objects dedtypesX;      // empty tiargs

                // https://issues.dlang.org/show_bug.cgi?id=11553
                // Check for recursive instantiation of tdx.
                for (TemplatePrevious* p = tdx.previous; p; p = p.prev)
                {
                    if (arrayObjectMatch(p.dedargs, &dedtypesX))
                    {
                        //printf("recursive, no match p.sc=%p %p %s\n", p.sc, this, this.toChars());
                        /* It must be a subscope of p.sc, other scope chains are not recursive
                         * instantiations.
                         */
                        for (Scope* scx = sc; scx; scx = scx.enclosing)
                        {
                            if (scx == p.sc)
                            {
                                error(loc, "recursive template expansion while looking for %s.%s", ti.toChars(), tdx.toChars());
                                goto Lerror;
                            }
                        }
                    }
                    /* BUG: should also check for ref param differences
                     */
                }

                TemplatePrevious pr;
                pr.prev = tdx.previous;
                pr.sc = sc;
                pr.dedargs = &dedtypesX;
                tdx.previous = &pr;             // add this to threaded list

                fd = resolveFuncCall(loc, sc, s, null, tthis, fargs, 1);

                tdx.previous = pr.prev;         // unlink from threaded list
            }
            else if (s.isFuncDeclaration())
            {
                fd = resolveFuncCall(loc, sc, s, null, tthis, fargs, 1);
            }
            else
                goto Lerror;

            if (!fd)
                return 0;

            if (fd.type.ty != Tfunction)
            {
                m.lastf = fd;   // to propagate "error match"
                m.count = 1;
                m.last = MATCHnomatch;
                return 1;
            }

            Type tthis_fd = fd.needThis() && !fd.isCtorDeclaration() ? tthis : null;

            auto tf = cast(TypeFunction)fd.type;
            MATCH mfa = tf.callMatch(tthis_fd, fargs);
            if (mfa < m.last)
                return 0;

            if (mta < ta_last) goto Ltd_best2;
            if (mta > ta_last) goto Ltd2;

            if (mfa < m.last) goto Ltd_best2;
            if (mfa > m.last) goto Ltd2;

        Lambig2:    // td_best and td are ambiguous
            //printf("Lambig2\n");
            m.nextf = fd;
            m.count++;
            return 0;

        Ltd_best2:
            return 0;

        Ltd2:
            // td is the new best match
            assert(td._scope);
            td_best = td;
            ti_best = null;
            property = 0;   // (backward compatibility)
            ta_last = mta;
            m.last = mfa;
            m.lastf = fd;
            tthis_best = tthis_fd;
            ov_index = 0;
            m.nextf = null;
            m.count = 1;
            return 0;
        }

        //printf("td = %s\n", td.toChars());
        for (size_t ovi = 0; f; f = f.overnext0, ovi++)
        {
            if (f.type.ty != Tfunction || f.errors)
                goto Lerror;

            /* This is a 'dummy' instance to evaluate constraint properly.
             */
            auto ti = new TemplateInstance(loc, td, tiargs);
            ti.parent = td.parent;  // Maybe calculating valid 'enclosing' is unnecessary.

            auto fd = f;
            int x = td.deduceFunctionTemplateMatch(ti, sc, fd, tthis, fargs);
            MATCH mta = cast(MATCH)(x >> 4);
            MATCH mfa = cast(MATCH)(x & 0xF);
            //printf("match:t/f = %d/%d\n", mta, mfa);
            if (!fd || mfa == MATCHnomatch)
                continue;

            Type tthis_fd = fd.needThis() ? tthis : null;

            bool isCtorCall = tthis_fd && fd.isCtorDeclaration();
            if (isCtorCall)
            {
                // Constructor call requires additional check.

                auto tf = cast(TypeFunction)fd.type;
                assert(tf.next);
                if (MODimplicitConv(tf.mod, tthis_fd.mod) ||
                    tf.isWild() && tf.isShared() == tthis_fd.isShared() ||
                    fd.isolateReturn())
                {
                    tthis_fd = null;
                }
                else
                    continue;   // MATCHnomatch
            }

            if (mta < ta_last) goto Ltd_best;
            if (mta > ta_last) goto Ltd;

            if (mfa < m.last) goto Ltd_best;
            if (mfa > m.last) goto Ltd;

            if (td_best)
            {
                // Disambiguate by picking the most specialized TemplateDeclaration
                MATCH c1 = td.leastAsSpecialized(sc, td_best, fargs);
                MATCH c2 = td_best.leastAsSpecialized(sc, td, fargs);
                //printf("1: c1 = %d, c2 = %d\n", c1, c2);
                if (c1 > c2) goto Ltd;
                if (c1 < c2) goto Ltd_best;
            }
            assert(fd && m.lastf);
            {
                // Disambiguate by tf.callMatch
                auto tf1 = cast(TypeFunction)fd.type;
                assert(tf1.ty == Tfunction);
                auto tf2 = cast(TypeFunction)m.lastf.type;
                assert(tf2.ty == Tfunction);
                MATCH c1 = tf1.callMatch(tthis_fd, fargs);
                MATCH c2 = tf2.callMatch(tthis_best, fargs);
                //printf("2: c1 = %d, c2 = %d\n", c1, c2);
                if (c1 > c2) goto Ltd;
                if (c1 < c2) goto Ltd_best;
            }
            {
                // Disambiguate by picking the most specialized FunctionDeclaration
                MATCH c1 = fd.leastAsSpecialized(m.lastf);
                MATCH c2 = m.lastf.leastAsSpecialized(fd);
                //printf("3: c1 = %d, c2 = %d\n", c1, c2);
                if (c1 > c2) goto Ltd;
                if (c1 < c2) goto Ltd_best;
            }

            // https://issues.dlang.org/show_bug.cgi?id=14450
            // Prefer exact qualified constructor for the creating object type
            if (isCtorCall && fd.type.mod != m.lastf.type.mod)
            {
                if (tthis.mod == fd.type.mod) goto Ltd;
                if (tthis.mod == m.lastf.type.mod) goto Ltd_best;
            }

            m.nextf = fd;
            m.count++;
            continue;

        Ltd_best:           // td_best is the best match so far
            //printf("Ltd_best\n");
            continue;

        Ltd:                // td is the new best match
            //printf("Ltd\n");
            assert(td._scope);
            td_best = td;
            ti_best = ti;
            property = 0;   // (backward compatibility)
            ta_last = mta;
            m.last = mfa;
            m.lastf = fd;
            tthis_best = tthis_fd;
            ov_index = ovi;
            m.nextf = null;
            m.count = 1;
            continue;
        }
        return 0;
    }

    auto td = dstart.isTemplateDeclaration();
    if (td && td.funcroot)
        dstart = td.funcroot;
    overloadApply(dstart, (Dsymbol s)
    {
        if (s.errors)
            return 0;
        if (auto fd = s.isFuncDeclaration())
            return applyFunction(fd);
        if (auto td = s.isTemplateDeclaration())
            return applyTemplate(td);
        return 0;
    });

    //printf("td_best = %p, m.lastf = %p\n", td_best, m.lastf);
    if (td_best && ti_best && m.count == 1)
    {
        // Matches to template function
        assert(td_best.onemember && td_best.onemember.isFuncDeclaration());
        /* The best match is td_best with arguments tdargs.
         * Now instantiate the template.
         */
        assert(td_best._scope);
        if (!sc)
            sc = td_best._scope; // workaround for Type.aliasthisOf

        auto ti = new TemplateInstance(loc, td_best, ti_best.tiargs);
        ti.semantic(sc, fargs);

        m.lastf = ti.toAlias().isFuncDeclaration();
        if (!m.lastf)
            goto Lnomatch;
        if (ti.errors)
        {
        Lerror:
            m.count = 1;
            assert(m.lastf);
            m.last = MATCHnomatch;
            return;
        }

        // look forward instantiated overload function
        // Dsymbol.oneMembers is alredy called in TemplateInstance.semantic.
        // it has filled overnext0d
        while (ov_index--)
        {
            m.lastf = m.lastf.overnext0;
            assert(m.lastf);
        }

        tthis_best = m.lastf.needThis() && !m.lastf.isCtorDeclaration() ? tthis : null;

        auto tf = cast(TypeFunction)m.lastf.type;
        if (tf.ty == Terror)
            goto Lerror;
        assert(tf.ty == Tfunction);
        if (!tf.callMatch(tthis_best, fargs))
            goto Lnomatch;

        /* As https://issues.dlang.org/show_bug.cgi?id=3682 shows,
         * a template instance can be matched while instantiating
         * that same template. Thus, the function type can be incomplete. Complete it.
         *
         * https://issues.dlang.org/show_bug.cgi?id=9208
         * For auto function, completion should be deferred to the end of
         * its semantic3. Should not complete it in here.
         */
        if (tf.next && !m.lastf.inferRetType)
        {
            m.lastf.type = tf.semantic(loc, sc);
        }
    }
    else if (m.lastf)
    {
        // Matches to non template function,
        // or found matches were ambiguous.
        assert(m.count >= 1);
    }
    else
    {
    Lnomatch:
        m.count = 0;
        m.lastf = null;
        m.last = MATCHnomatch;
    }
}

/* ======================== Type ============================================ */

/****
 * Given an identifier, figure out which TemplateParameter it is.
 * Return IDX_NOTFOUND if not found.
 */
private size_t templateIdentifierLookup(Identifier id, TemplateParameters* parameters)
{
    for (size_t i = 0; i < parameters.dim; i++)
    {
        TemplateParameter tp = (*parameters)[i];
        if (tp.ident.equals(id))
            return i;
    }
    return IDX_NOTFOUND;
}

private size_t templateParameterLookup(Type tparam, TemplateParameters* parameters)
{
    if (tparam.ty == Tident)
    {
        TypeIdentifier tident = cast(TypeIdentifier)tparam;
        //printf("\ttident = '%s'\n", tident.toChars());
        return templateIdentifierLookup(tident.ident, parameters);
    }
    return IDX_NOTFOUND;
}

private ubyte deduceWildHelper(Type t, Type* at, Type tparam)
{
    if ((tparam.mod & MODwild) == 0)
        return 0;

    *at = null;

    auto X(T, U)(T U, U T)
    {
        return (U << 4) | T;
    }

    switch (X(tparam.mod, t.mod))
    {
    case X(MODwild, 0):
    case X(MODwild, MODconst):
    case X(MODwild, MODshared):
    case X(MODwild, MODshared | MODconst):
    case X(MODwild, MODimmutable):
    case X(MODwildconst, 0):
    case X(MODwildconst, MODconst):
    case X(MODwildconst, MODshared):
    case X(MODwildconst, MODshared | MODconst):
    case X(MODwildconst, MODimmutable):
    case X(MODshared | MODwild, MODshared):
    case X(MODshared | MODwild, MODshared | MODconst):
    case X(MODshared | MODwild, MODimmutable):
    case X(MODshared | MODwildconst, MODshared):
    case X(MODshared | MODwildconst, MODshared | MODconst):
    case X(MODshared | MODwildconst, MODimmutable):
        {
            ubyte wm = (t.mod & ~MODshared);
            if (wm == 0)
                wm = MODmutable;
            ubyte m = (t.mod & (MODconst | MODimmutable)) | (tparam.mod & t.mod & MODshared);
            *at = t.unqualify(m);
            return wm;
        }
    case X(MODwild, MODwild):
    case X(MODwild, MODwildconst):
    case X(MODwild, MODshared | MODwild):
    case X(MODwild, MODshared | MODwildconst):
    case X(MODwildconst, MODwild):
    case X(MODwildconst, MODwildconst):
    case X(MODwildconst, MODshared | MODwild):
    case X(MODwildconst, MODshared | MODwildconst):
    case X(MODshared | MODwild, MODshared | MODwild):
    case X(MODshared | MODwild, MODshared | MODwildconst):
    case X(MODshared | MODwildconst, MODshared | MODwild):
    case X(MODshared | MODwildconst, MODshared | MODwildconst):
        {
            *at = t.unqualify(tparam.mod & t.mod);
            return MODwild;
        }
    default:
        return 0;
    }
}

private MATCH deduceTypeHelper(Type t, Type* at, Type tparam)
{
    // 9*9 == 81 cases

    auto X(T, U)(T U, U T)
    {
        return (U << 4) | T;
    }

    switch (X(tparam.mod, t.mod))
    {
    case X(0, 0):
    case X(0, MODconst):
    case X(0, MODwild):
    case X(0, MODwildconst):
    case X(0, MODshared):
    case X(0, MODshared | MODconst):
    case X(0, MODshared | MODwild):
    case X(0, MODshared | MODwildconst):
    case X(0, MODimmutable):
        // foo(U)                       T                       => T
        // foo(U)                       const(T)                => const(T)
        // foo(U)                       inout(T)                => inout(T)
        // foo(U)                       inout(const(T))         => inout(const(T))
        // foo(U)                       shared(T)               => shared(T)
        // foo(U)                       shared(const(T))        => shared(const(T))
        // foo(U)                       shared(inout(T))        => shared(inout(T))
        // foo(U)                       shared(inout(const(T))) => shared(inout(const(T)))
        // foo(U)                       immutable(T)            => immutable(T)
        {
            *at = t;
            return MATCHexact;
        }
    case X(MODconst, MODconst):
    case X(MODwild, MODwild):
    case X(MODwildconst, MODwildconst):
    case X(MODshared, MODshared):
    case X(MODshared | MODconst, MODshared | MODconst):
    case X(MODshared | MODwild, MODshared | MODwild):
    case X(MODshared | MODwildconst, MODshared | MODwildconst):
    case X(MODimmutable, MODimmutable):
        // foo(const(U))                const(T)                => T
        // foo(inout(U))                inout(T)                => T
        // foo(inout(const(U)))         inout(const(T))         => T
        // foo(shared(U))               shared(T)               => T
        // foo(shared(const(U)))        shared(const(T))        => T
        // foo(shared(inout(U)))        shared(inout(T))        => T
        // foo(shared(inout(const(U)))) shared(inout(const(T))) => T
        // foo(immutable(U))            immutable(T)            => T
        {
            *at = t.mutableOf().unSharedOf();
            return MATCHexact;
        }
    case X(MODconst, 0):
    case X(MODconst, MODwild):
    case X(MODconst, MODwildconst):
    case X(MODconst, MODshared | MODconst):
    case X(MODconst, MODshared | MODwild):
    case X(MODconst, MODshared | MODwildconst):
    case X(MODconst, MODimmutable):
    case X(MODwild, MODshared | MODwild):
    case X(MODwildconst, MODshared | MODwildconst):
    case X(MODshared | MODconst, MODimmutable):
        // foo(const(U))                T                       => T
        // foo(const(U))                inout(T)                => T
        // foo(const(U))                inout(const(T))         => T
        // foo(const(U))                shared(const(T))        => shared(T)
        // foo(const(U))                shared(inout(T))        => shared(T)
        // foo(const(U))                shared(inout(const(T))) => shared(T)
        // foo(const(U))                immutable(T)            => T
        // foo(inout(U))                shared(inout(T))        => shared(T)
        // foo(inout(const(U)))         shared(inout(const(T))) => shared(T)
        // foo(shared(const(U)))        immutable(T)            => T
        {
            *at = t.mutableOf();
            return MATCHconst;
        }
    case X(MODconst, MODshared):
        // foo(const(U))                shared(T)               => shared(T)
        {
            *at = t;
            return MATCHconst;
        }
    case X(MODshared, MODshared | MODconst):
    case X(MODshared, MODshared | MODwild):
    case X(MODshared, MODshared | MODwildconst):
    case X(MODshared | MODconst, MODshared):
        // foo(shared(U))               shared(const(T))        => const(T)
        // foo(shared(U))               shared(inout(T))        => inout(T)
        // foo(shared(U))               shared(inout(const(T))) => inout(const(T))
        // foo(shared(const(U)))        shared(T)               => T
        {
            *at = t.unSharedOf();
            return MATCHconst;
        }
    case X(MODwildconst, MODimmutable):
    case X(MODshared | MODconst, MODshared | MODwildconst):
    case X(MODshared | MODwildconst, MODimmutable):
    case X(MODshared | MODwildconst, MODshared | MODwild):
        // foo(inout(const(U)))         immutable(T)            => T
        // foo(shared(const(U)))        shared(inout(const(T))) => T
        // foo(shared(inout(const(U)))) immutable(T)            => T
        // foo(shared(inout(const(U)))) shared(inout(T))        => T
        {
            *at = t.unSharedOf().mutableOf();
            return MATCHconst;
        }
    case X(MODshared | MODconst, MODshared | MODwild):
        // foo(shared(const(U)))        shared(inout(T))        => T
        {
            *at = t.unSharedOf().mutableOf();
            return MATCHconst;
        }
    case X(MODwild, 0):
    case X(MODwild, MODconst):
    case X(MODwild, MODwildconst):
    case X(MODwild, MODimmutable):
    case X(MODwild, MODshared):
    case X(MODwild, MODshared | MODconst):
    case X(MODwild, MODshared | MODwildconst):
    case X(MODwildconst, 0):
    case X(MODwildconst, MODconst):
    case X(MODwildconst, MODwild):
    case X(MODwildconst, MODshared):
    case X(MODwildconst, MODshared | MODconst):
    case X(MODwildconst, MODshared | MODwild):
    case X(MODshared, 0):
    case X(MODshared, MODconst):
    case X(MODshared, MODwild):
    case X(MODshared, MODwildconst):
    case X(MODshared, MODimmutable):
    case X(MODshared | MODconst, 0):
    case X(MODshared | MODconst, MODconst):
    case X(MODshared | MODconst, MODwild):
    case X(MODshared | MODconst, MODwildconst):
    case X(MODshared | MODwild, 0):
    case X(MODshared | MODwild, MODconst):
    case X(MODshared | MODwild, MODwild):
    case X(MODshared | MODwild, MODwildconst):
    case X(MODshared | MODwild, MODimmutable):
    case X(MODshared | MODwild, MODshared):
    case X(MODshared | MODwild, MODshared | MODconst):
    case X(MODshared | MODwild, MODshared | MODwildconst):
    case X(MODshared | MODwildconst, 0):
    case X(MODshared | MODwildconst, MODconst):
    case X(MODshared | MODwildconst, MODwild):
    case X(MODshared | MODwildconst, MODwildconst):
    case X(MODshared | MODwildconst, MODshared):
    case X(MODshared | MODwildconst, MODshared | MODconst):
    case X(MODimmutable, 0):
    case X(MODimmutable, MODconst):
    case X(MODimmutable, MODwild):
    case X(MODimmutable, MODwildconst):
    case X(MODimmutable, MODshared):
    case X(MODimmutable, MODshared | MODconst):
    case X(MODimmutable, MODshared | MODwild):
    case X(MODimmutable, MODshared | MODwildconst):
        // foo(inout(U))                T                       => nomatch
        // foo(inout(U))                const(T)                => nomatch
        // foo(inout(U))                inout(const(T))         => nomatch
        // foo(inout(U))                immutable(T)            => nomatch
        // foo(inout(U))                shared(T)               => nomatch
        // foo(inout(U))                shared(const(T))        => nomatch
        // foo(inout(U))                shared(inout(const(T))) => nomatch
        // foo(inout(const(U)))         T                       => nomatch
        // foo(inout(const(U)))         const(T)                => nomatch
        // foo(inout(const(U)))         inout(T)                => nomatch
        // foo(inout(const(U)))         shared(T)               => nomatch
        // foo(inout(const(U)))         shared(const(T))        => nomatch
        // foo(inout(const(U)))         shared(inout(T))        => nomatch
        // foo(shared(U))               T                       => nomatch
        // foo(shared(U))               const(T)                => nomatch
        // foo(shared(U))               inout(T)                => nomatch
        // foo(shared(U))               inout(const(T))         => nomatch
        // foo(shared(U))               immutable(T)            => nomatch
        // foo(shared(const(U)))        T                       => nomatch
        // foo(shared(const(U)))        const(T)                => nomatch
        // foo(shared(const(U)))        inout(T)                => nomatch
        // foo(shared(const(U)))        inout(const(T))         => nomatch
        // foo(shared(inout(U)))        T                       => nomatch
        // foo(shared(inout(U)))        const(T)                => nomatch
        // foo(shared(inout(U)))        inout(T)                => nomatch
        // foo(shared(inout(U)))        inout(const(T))         => nomatch
        // foo(shared(inout(U)))        immutable(T)            => nomatch
        // foo(shared(inout(U)))        shared(T)               => nomatch
        // foo(shared(inout(U)))        shared(const(T))        => nomatch
        // foo(shared(inout(U)))        shared(inout(const(T))) => nomatch
        // foo(shared(inout(const(U)))) T                       => nomatch
        // foo(shared(inout(const(U)))) const(T)                => nomatch
        // foo(shared(inout(const(U)))) inout(T)                => nomatch
        // foo(shared(inout(const(U)))) inout(const(T))         => nomatch
        // foo(shared(inout(const(U)))) shared(T)               => nomatch
        // foo(shared(inout(const(U)))) shared(const(T))        => nomatch
        // foo(immutable(U))            T                       => nomatch
        // foo(immutable(U))            const(T)                => nomatch
        // foo(immutable(U))            inout(T)                => nomatch
        // foo(immutable(U))            inout(const(T))         => nomatch
        // foo(immutable(U))            shared(T)               => nomatch
        // foo(immutable(U))            shared(const(T))        => nomatch
        // foo(immutable(U))            shared(inout(T))        => nomatch
        // foo(immutable(U))            shared(inout(const(T))) => nomatch
        return MATCHnomatch;

    default:
        assert(0);
    }
}

__gshared Expression emptyArrayElement = null;

/* These form the heart of template argument deduction.
 * Given 'this' being the type argument to the template instance,
 * it is matched against the template declaration parameter specialization
 * 'tparam' to determine the type to be used for the parameter.
 * Example:
 *      template Foo(T:T*)      // template declaration
 *      Foo!(int*)              // template instantiation
 * Input:
 *      this = int*
 *      tparam = T*
 *      parameters = [ T:T* ]   // Array of TemplateParameter's
 * Output:
 *      dedtypes = [ int ]      // Array of Expression/Type's
 */
MATCH deduceType(RootObject o, Scope* sc, Type tparam, TemplateParameters* parameters, Objects* dedtypes, uint* wm = null, size_t inferStart = 0)
{
    extern (C++) final class DeduceType : Visitor
    {
        alias visit = super.visit;
    public:
        Scope* sc;
        Type tparam;
        TemplateParameters* parameters;
        Objects* dedtypes;
        uint* wm;
        size_t inferStart;
        MATCH result;

        extern (D) this(Scope* sc, Type tparam, TemplateParameters* parameters, Objects* dedtypes, uint* wm, size_t inferStart)
        {
            this.sc = sc;
            this.tparam = tparam;
            this.parameters = parameters;
            this.dedtypes = dedtypes;
            this.wm = wm;
            this.inferStart = inferStart;
            result = MATCHnomatch;
        }

        override void visit(Type t)
        {
            version (none)
            {
                printf("Type.deduceType()\n");
                printf("\tthis   = %d, ", t.ty);
                t.print();
                printf("\ttparam = %d, ", tparam.ty);
                tparam.print();
            }
            if (!tparam)
                goto Lnomatch;

            if (t == tparam)
                goto Lexact;

            if (tparam.ty == Tident)
            {
                // Determine which parameter tparam is
                size_t i = templateParameterLookup(tparam, parameters);
                if (i == IDX_NOTFOUND)
                {
                    if (!sc)
                        goto Lnomatch;

                    /* Need a loc to go with the semantic routine.
                     */
                    Loc loc;
                    if (parameters.dim)
                    {
                        TemplateParameter tp = (*parameters)[0];
                        loc = tp.loc;
                    }

                    /* BUG: what if tparam is a template instance, that
                     * has as an argument another Tident?
                     */
                    tparam = tparam.semantic(loc, sc);
                    assert(tparam.ty != Tident);
                    result = deduceType(t, sc, tparam, parameters, dedtypes, wm);
                    return;
                }

                TemplateParameter tp = (*parameters)[i];

                TypeIdentifier tident = cast(TypeIdentifier)tparam;
                if (tident.idents.dim > 0)
                {
                    //printf("matching %s to %s\n", tparam.toChars(), t.toChars());
                    Dsymbol s = t.toDsymbol(sc);
                    for (size_t j = tident.idents.dim; j-- > 0;)
                    {
                        RootObject id = tident.idents[j];
                        if (id.dyncast() == DYNCAST.identifier)
                        {
                            if (!s || !s.parent)
                                goto Lnomatch;
                            Dsymbol s2 = s.parent.search(Loc(), cast(Identifier)id);
                            if (!s2)
                                goto Lnomatch;
                            s2 = s2.toAlias();
                            //printf("[%d] s = %s %s, s2 = %s %s\n", j, s.kind(), s.toChars(), s2.kind(), s2.toChars());
                            if (s != s2)
                            {
                                if (Type tx = s2.getType())
                                {
                                    if (s != tx.toDsymbol(sc))
                                        goto Lnomatch;
                                }
                                else
                                    goto Lnomatch;
                            }
                            s = s.parent;
                        }
                        else
                            goto Lnomatch;
                    }
                    //printf("[e] s = %s\n", s?s.toChars():"(null)");
                    if (tp.isTemplateTypeParameter())
                    {
                        Type tt = s.getType();
                        if (!tt)
                            goto Lnomatch;
                        Type at = cast(Type)(*dedtypes)[i];
                        if (at && at.ty == Tnone)
                            at = (cast(TypeDeduced)at).tded;
                        if (!at || tt.equals(at))
                        {
                            (*dedtypes)[i] = tt;
                            goto Lexact;
                        }
                    }
                    if (tp.isTemplateAliasParameter())
                    {
                        Dsymbol s2 = cast(Dsymbol)(*dedtypes)[i];
                        if (!s2 || s == s2)
                        {
                            (*dedtypes)[i] = s;
                            goto Lexact;
                        }
                    }
                    goto Lnomatch;
                }

                // Found the corresponding parameter tp
                if (!tp.isTemplateTypeParameter())
                    goto Lnomatch;

                Type at = cast(Type)(*dedtypes)[i];
                Type tt;
                if (ubyte wx = wm ? deduceWildHelper(t, &tt, tparam) : 0)
                {
                    // type vs (none)
                    if (!at)
                    {
                        (*dedtypes)[i] = tt;
                        *wm |= wx;
                        result = MATCHconst;
                        return;
                    }

                    // type vs expressions
                    if (at.ty == Tnone)
                    {
                        TypeDeduced xt = cast(TypeDeduced)at;
                        result = xt.matchAll(tt);
                        if (result > MATCHnomatch)
                        {
                            (*dedtypes)[i] = tt;
                            if (result > MATCHconst)
                                result = MATCHconst; // limit level for inout matches
                        }
                        return;
                    }

                    // type vs type
                    if (tt.equals(at))
                    {
                        (*dedtypes)[i] = tt; // Prefer current type match
                        goto Lconst;
                    }
                    if (tt.implicitConvTo(at.constOf()))
                    {
                        (*dedtypes)[i] = at.constOf().mutableOf();
                        *wm |= MODconst;
                        goto Lconst;
                    }
                    if (at.implicitConvTo(tt.constOf()))
                    {
                        (*dedtypes)[i] = tt.constOf().mutableOf();
                        *wm |= MODconst;
                        goto Lconst;
                    }
                    goto Lnomatch;
                }
                else if (MATCH m = deduceTypeHelper(t, &tt, tparam))
                {
                    // type vs (none)
                    if (!at)
                    {
                        (*dedtypes)[i] = tt;
                        result = m;
                        return;
                    }

                    // type vs expressions
                    if (at.ty == Tnone)
                    {
                        TypeDeduced xt = cast(TypeDeduced)at;
                        result = xt.matchAll(tt);
                        if (result > MATCHnomatch)
                        {
                            (*dedtypes)[i] = tt;
                        }
                        return;
                    }

                    // type vs type
                    if (tt.equals(at))
                    {
                        goto Lexact;
                    }
                    if (tt.ty == Tclass && at.ty == Tclass)
                    {
                        result = tt.implicitConvTo(at);
                        return;
                    }
                    if (tt.ty == Tsarray && at.ty == Tarray && tt.nextOf().implicitConvTo(at.nextOf()) >= MATCHconst)
                    {
                        goto Lexact;
                    }
                }
                goto Lnomatch;
            }

            if (tparam.ty == Ttypeof)
            {
                /* Need a loc to go with the semantic routine.
                 */
                Loc loc;
                if (parameters.dim)
                {
                    TemplateParameter tp = (*parameters)[0];
                    loc = tp.loc;
                }

                tparam = tparam.semantic(loc, sc);
            }
            if (t.ty != tparam.ty)
            {
                if (Dsymbol sym = t.toDsymbol(sc))
                {
                    if (sym.isforwardRef() && !tparam.deco)
                        goto Lnomatch;
                }

                MATCH m = t.implicitConvTo(tparam);
                if (m == MATCHnomatch)
                {
                    if (t.ty == Tclass)
                    {
                        TypeClass tc = cast(TypeClass)t;
                        if (tc.sym.aliasthis && !(tc.att & RECtracingDT))
                        {
                            tc.att = cast(AliasThisRec)(tc.att | RECtracingDT);
                            m = deduceType(t.aliasthisOf(), sc, tparam, parameters, dedtypes, wm);
                            tc.att = cast(AliasThisRec)(tc.att & ~RECtracingDT);
                        }
                    }
                    else if (t.ty == Tstruct)
                    {
                        TypeStruct ts = cast(TypeStruct)t;
                        if (ts.sym.aliasthis && !(ts.att & RECtracingDT))
                        {
                            ts.att = cast(AliasThisRec)(ts.att | RECtracingDT);
                            m = deduceType(t.aliasthisOf(), sc, tparam, parameters, dedtypes, wm);
                            ts.att = cast(AliasThisRec)(ts.att & ~RECtracingDT);
                        }
                    }
                }
                result = m;
                return;
            }

            if (t.nextOf())
            {
                if (tparam.deco && !tparam.hasWild())
                {
                    result = t.implicitConvTo(tparam);
                    return;
                }

                Type tpn = tparam.nextOf();
                if (wm && t.ty == Taarray && tparam.isWild())
                {
                    // https://issues.dlang.org/show_bug.cgi?id=12403
                    // In IFTI, stop inout matching on transitive part of AA types.
                    tpn = tpn.substWildTo(MODmutable);
                }

                result = deduceType(t.nextOf(), sc, tpn, parameters, dedtypes, wm);
                return;
            }

        Lexact:
            result = MATCHexact;
            return;

        Lnomatch:
            result = MATCHnomatch;
            return;

        Lconst:
            result = MATCHconst;
        }

        override void visit(TypeVector t)
        {
            version (none)
            {
                printf("TypeVector.deduceType()\n");
                printf("\tthis   = %d, ", t.ty);
                t.print();
                printf("\ttparam = %d, ", tparam.ty);
                tparam.print();
            }
            if (tparam.ty == Tvector)
            {
                TypeVector tp = cast(TypeVector)tparam;
                result = deduceType(t.basetype, sc, tp.basetype, parameters, dedtypes, wm);
                return;
            }
            visit(cast(Type)t);
        }

        override void visit(TypeDArray t)
        {
            version (none)
            {
                printf("TypeDArray.deduceType()\n");
                printf("\tthis   = %d, ", t.ty);
                t.print();
                printf("\ttparam = %d, ", tparam.ty);
                tparam.print();
            }
            visit(cast(Type)t);
        }

        override void visit(TypeSArray t)
        {
            version (none)
            {
                printf("TypeSArray.deduceType()\n");
                printf("\tthis   = %d, ", t.ty);
                t.print();
                printf("\ttparam = %d, ", tparam.ty);
                tparam.print();
            }

            // Extra check that array dimensions must match
            if (tparam)
            {
                if (tparam.ty == Tarray)
                {
                    MATCH m = deduceType(t.next, sc, tparam.nextOf(), parameters, dedtypes, wm);
                    result = (m >= MATCHconst) ? MATCHconvert : MATCHnomatch;
                    return;
                }

                TemplateParameter tp = null;
                Expression edim = null;
                size_t i;
                if (tparam.ty == Tsarray)
                {
                    TypeSArray tsa = cast(TypeSArray)tparam;
                    if (tsa.dim.op == TOKvar && (cast(VarExp)tsa.dim).var.storage_class & STCtemplateparameter)
                    {
                        Identifier id = (cast(VarExp)tsa.dim).var.ident;
                        i = templateIdentifierLookup(id, parameters);
                        assert(i != IDX_NOTFOUND);
                        tp = (*parameters)[i];
                    }
                    else
                        edim = tsa.dim;
                }
                else if (tparam.ty == Taarray)
                {
                    TypeAArray taa = cast(TypeAArray)tparam;
                    i = templateParameterLookup(taa.index, parameters);
                    if (i != IDX_NOTFOUND)
                        tp = (*parameters)[i];
                    else
                    {
                        Expression e;
                        Type tx;
                        Dsymbol s;
                        taa.index.resolve(Loc(), sc, &e, &tx, &s);
                        edim = s ? getValue(s) : getValue(e);
                    }
                }
                if (tp && tp.matchArg(sc, t.dim, i, parameters, dedtypes, null) || edim && edim.toInteger() == t.dim.toInteger())
                {
                    result = deduceType(t.next, sc, tparam.nextOf(), parameters, dedtypes, wm);
                    return;
                }
            }
            visit(cast(Type)t);
        }

        override void visit(TypeAArray t)
        {
            version (none)
            {
                printf("TypeAArray.deduceType()\n");
                printf("\tthis   = %d, ", t.ty);
                t.print();
                printf("\ttparam = %d, ", tparam.ty);
                tparam.print();
            }

            // Extra check that index type must match
            if (tparam && tparam.ty == Taarray)
            {
                TypeAArray tp = cast(TypeAArray)tparam;
                if (!deduceType(t.index, sc, tp.index, parameters, dedtypes))
                {
                    result = MATCHnomatch;
                    return;
                }
            }
            visit(cast(Type)t);
        }

        override void visit(TypeFunction t)
        {
            //printf("TypeFunction.deduceType()\n");
            //printf("\tthis   = %d, ", t.ty); t.print();
            //printf("\ttparam = %d, ", tparam.ty); tparam.print();

            // Extra check that function characteristics must match
            if (tparam && tparam.ty == Tfunction)
            {
                TypeFunction tp = cast(TypeFunction)tparam;
                if (t.varargs != tp.varargs || t.linkage != tp.linkage)
                {
                    result = MATCHnomatch;
                    return;
                }

                size_t nfargs = Parameter.dim(t.parameters);
                size_t nfparams = Parameter.dim(tp.parameters);

                // https://issues.dlang.org/show_bug.cgi?id=2579
                // Apply function parameter storage classes to parameter types
                for (size_t i = 0; i < nfparams; i++)
                {
                    Parameter fparam = Parameter.getNth(tp.parameters, i);
                    fparam.type = fparam.type.addStorageClass(fparam.storageClass);
                    fparam.storageClass &= ~(STC_TYPECTOR | STCin);
                }
                //printf("\t. this   = %d, ", t.ty); t.print();
                //printf("\t. tparam = %d, ", tparam.ty); tparam.print();

                /* See if tuple match
                 */
                if (nfparams > 0 && nfargs >= nfparams - 1)
                {
                    /* See if 'A' of the template parameter matches 'A'
                     * of the type of the last function parameter.
                     */
                    Parameter fparam = Parameter.getNth(tp.parameters, nfparams - 1);
                    assert(fparam);
                    assert(fparam.type);
                    if (fparam.type.ty != Tident)
                        goto L1;
                    TypeIdentifier tid = cast(TypeIdentifier)fparam.type;
                    if (tid.idents.dim)
                        goto L1;

                    /* Look through parameters to find tuple matching tid.ident
                     */
                    size_t tupi = 0;
                    for (; 1; tupi++)
                    {
                        if (tupi == parameters.dim)
                            goto L1;
                        TemplateParameter tx = (*parameters)[tupi];
                        TemplateTupleParameter tup = tx.isTemplateTupleParameter();
                        if (tup && tup.ident.equals(tid.ident))
                            break;
                    }

                    /* The types of the function arguments [nfparams - 1 .. nfargs]
                     * now form the tuple argument.
                     */
                    size_t tuple_dim = nfargs - (nfparams - 1);

                    /* See if existing tuple, and whether it matches or not
                     */
                    RootObject o = (*dedtypes)[tupi];
                    if (o)
                    {
                        // Existing deduced argument must be a tuple, and must match
                        Tuple tup = isTuple(o);
                        if (!tup || tup.objects.dim != tuple_dim)
                        {
                            result = MATCHnomatch;
                            return;
                        }
                        for (size_t i = 0; i < tuple_dim; i++)
                        {
                            Parameter arg = Parameter.getNth(t.parameters, nfparams - 1 + i);
                            if (!arg.type.equals(tup.objects[i]))
                            {
                                result = MATCHnomatch;
                                return;
                            }
                        }
                    }
                    else
                    {
                        // Create new tuple
                        auto tup = new Tuple();
                        tup.objects.setDim(tuple_dim);
                        for (size_t i = 0; i < tuple_dim; i++)
                        {
                            Parameter arg = Parameter.getNth(t.parameters, nfparams - 1 + i);
                            tup.objects[i] = arg.type;
                        }
                        (*dedtypes)[tupi] = tup;
                    }
                    nfparams--; // don't consider the last parameter for type deduction
                    goto L2;
                }

            L1:
                if (nfargs != nfparams)
                {
                    result = MATCHnomatch;
                    return;
                }
            L2:
                for (size_t i = 0; i < nfparams; i++)
                {
                    Parameter a = Parameter.getNth(t.parameters, i);
                    Parameter ap = Parameter.getNth(tp.parameters, i);

                    if (!a.isCovariant(t.isref, ap) ||
                        !deduceType(a.type, sc, ap.type, parameters, dedtypes))
                    {
                        result = MATCHnomatch;
                        return;
                    }
                }
            }
            visit(cast(Type)t);
        }

        override void visit(TypeIdentifier t)
        {
            // Extra check
            if (tparam && tparam.ty == Tident)
            {
                TypeIdentifier tp = cast(TypeIdentifier)tparam;
                for (size_t i = 0; i < t.idents.dim; i++)
                {
                    RootObject id1 = t.idents[i];
                    RootObject id2 = tp.idents[i];
                    if (!id1.equals(id2))
                    {
                        result = MATCHnomatch;
                        return;
                    }
                }
            }
            visit(cast(Type)t);
        }

        override void visit(TypeInstance t)
        {
            version (none)
            {
                printf("TypeInstance.deduceType()\n");
                printf("\tthis   = %d, ", t.ty);
                t.print();
                printf("\ttparam = %d, ", tparam.ty);
                tparam.print();
            }
            // Extra check
            if (tparam && tparam.ty == Tinstance && t.tempinst.tempdecl)
            {
                TemplateDeclaration tempdecl = t.tempinst.tempdecl.isTemplateDeclaration();
                assert(tempdecl);

                TypeInstance tp = cast(TypeInstance)tparam;

                //printf("tempinst.tempdecl = %p\n", tempdecl);
                //printf("tp.tempinst.tempdecl = %p\n", tp.tempinst.tempdecl);
                if (!tp.tempinst.tempdecl)
                {
                    //printf("tp.tempinst.name = '%s'\n", tp.tempinst.name.toChars());

                    /* Handle case of:
                     *  template Foo(T : sa!(T), alias sa)
                     */
                    size_t i = templateIdentifierLookup(tp.tempinst.name, parameters);
                    if (i == IDX_NOTFOUND)
                    {
                        /* Didn't find it as a parameter identifier. Try looking
                         * it up and seeing if is an alias.
                         * https://issues.dlang.org/show_bug.cgi?id=1454
                         */
                        auto tid = new TypeIdentifier(tp.loc, tp.tempinst.name);
                        Type tx;
                        Expression e;
                        Dsymbol s;
                        tid.resolve(tp.loc, sc, &e, &tx, &s);
                        if (tx)
                        {
                            s = tx.toDsymbol(sc);
                            if (TemplateInstance ti = s ? s.parent.isTemplateInstance() : null)
                            {
                                // https://issues.dlang.org/show_bug.cgi?id=14290
                                // Try to match with ti.tempecl,
                                // only when ti is an enclosing instance.
                                Dsymbol p = sc.parent;
                                while (p && p != ti)
                                    p = p.parent;
                                if (p)
                                    s = ti.tempdecl;
                            }
                        }
                        if (s)
                        {
                            s = s.toAlias();
                            TemplateDeclaration td = s.isTemplateDeclaration();
                            if (td)
                            {
                                if (td.overroot)
                                    td = td.overroot;
                                for (; td; td = td.overnext)
                                {
                                    if (td == tempdecl)
                                        goto L2;
                                }
                            }
                        }
                        goto Lnomatch;
                    }
                    TemplateParameter tpx = (*parameters)[i];
                    if (!tpx.matchArg(sc, tempdecl, i, parameters, dedtypes, null))
                        goto Lnomatch;
                }
                else if (tempdecl != tp.tempinst.tempdecl)
                    goto Lnomatch;

            L2:
                for (size_t i = 0; 1; i++)
                {
                    //printf("\ttest: tempinst.tiargs[%d]\n", i);
                    RootObject o1 = null;
                    if (i < t.tempinst.tiargs.dim)
                        o1 = (*t.tempinst.tiargs)[i];
                    else if (i < t.tempinst.tdtypes.dim && i < tp.tempinst.tiargs.dim)
                    {
                        // Pick up default arg
                        o1 = t.tempinst.tdtypes[i];
                    }
                    else if (i >= tp.tempinst.tiargs.dim)
                        break;

                    if (i >= tp.tempinst.tiargs.dim)
                    {
                        size_t dim = tempdecl.parameters.dim - (tempdecl.isVariadic() ? 1 : 0);
                        while (i < dim && ((*tempdecl.parameters)[i].dependent || (*tempdecl.parameters)[i].hasDefaultArg()))
                        {
                            i++;
                        }
                        if (i >= dim)
                            break; // match if all remained parameters are dependent
                        goto Lnomatch;
                    }

                    RootObject o2 = (*tp.tempinst.tiargs)[i];
                    Type t2 = isType(o2);

                    size_t j = (t2 && t2.ty == Tident && i == tp.tempinst.tiargs.dim - 1)
                        ? templateParameterLookup(t2, parameters) : IDX_NOTFOUND;
                    if (j != IDX_NOTFOUND && j == parameters.dim - 1 &&
                        (*parameters)[j].isTemplateTupleParameter())
                    {
                        /* Given:
                         *  struct A(B...) {}
                         *  alias A!(int, float) X;
                         *  static if (is(X Y == A!(Z), Z...)) {}
                         * deduce that Z is a tuple(int, float)
                         */

                        /* Create tuple from remaining args
                         */
                        auto vt = new Tuple();
                        size_t vtdim = (tempdecl.isVariadic() ? t.tempinst.tiargs.dim : t.tempinst.tdtypes.dim) - i;
                        vt.objects.setDim(vtdim);
                        for (size_t k = 0; k < vtdim; k++)
                        {
                            RootObject o;
                            if (k < t.tempinst.tiargs.dim)
                                o = (*t.tempinst.tiargs)[i + k];
                            else // Pick up default arg
                                o = t.tempinst.tdtypes[i + k];
                            vt.objects[k] = o;
                        }

                        Tuple v = cast(Tuple)(*dedtypes)[j];
                        if (v)
                        {
                            if (!match(v, vt))
                                goto Lnomatch;
                        }
                        else
                            (*dedtypes)[j] = vt;
                        break;
                    }
                    else if (!o1)
                        break;

                    Type t1 = isType(o1);
                    Dsymbol s1 = isDsymbol(o1);
                    Dsymbol s2 = isDsymbol(o2);
                    Expression e1 = s1 ? getValue(s1) : getValue(isExpression(o1));
                    Expression e2 = isExpression(o2);
                    version (none)
                    {
                        Tuple v1 = isTuple(o1);
                        Tuple v2 = isTuple(o2);
                        if (t1)
                            printf("t1 = %s\n", t1.toChars());
                        if (t2)
                            printf("t2 = %s\n", t2.toChars());
                        if (e1)
                            printf("e1 = %s\n", e1.toChars());
                        if (e2)
                            printf("e2 = %s\n", e2.toChars());
                        if (s1)
                            printf("s1 = %s\n", s1.toChars());
                        if (s2)
                            printf("s2 = %s\n", s2.toChars());
                        if (v1)
                            printf("v1 = %s\n", v1.toChars());
                        if (v2)
                            printf("v2 = %s\n", v2.toChars());
                    }

                    if (t1 && t2)
                    {
                        if (!deduceType(t1, sc, t2, parameters, dedtypes))
                            goto Lnomatch;
                    }
                    else if (e1 && e2)
                    {
                    Le:
                        e1 = e1.ctfeInterpret();

                        /* If it is one of the template parameters for this template,
                         * we should not attempt to interpret it. It already has a value.
                         */
                        if (e2.op == TOKvar && ((cast(VarExp)e2).var.storage_class & STCtemplateparameter))
                        {
                            /*
                             * (T:Number!(e2), int e2)
                             */
                            j = templateIdentifierLookup((cast(VarExp)e2).var.ident, parameters);
                            if (j != IDX_NOTFOUND)
                                goto L1;
                            // The template parameter was not from this template
                            // (it may be from a parent template, for example)
                        }

                        e2 = e2.semantic(sc); // https://issues.dlang.org/show_bug.cgi?id=13417
                        e2 = e2.ctfeInterpret();

                        //printf("e1 = %s, type = %s %d\n", e1.toChars(), e1.type.toChars(), e1.type.ty);
                        //printf("e2 = %s, type = %s %d\n", e2.toChars(), e2.type.toChars(), e2.type.ty);
                        if (!e1.equals(e2))
                        {
                            if (!e2.implicitConvTo(e1.type))
                                goto Lnomatch;

                            e2 = e2.implicitCastTo(sc, e1.type);
                            e2 = e2.ctfeInterpret();
                            if (!e1.equals(e2))
                                goto Lnomatch;
                        }
                    }
                    else if (e1 && t2 && t2.ty == Tident)
                    {
                        j = templateParameterLookup(t2, parameters);
                    L1:
                        if (j == IDX_NOTFOUND)
                        {
                            t2.resolve((cast(TypeIdentifier)t2).loc, sc, &e2, &t2, &s2);
                            if (e2)
                                goto Le;
                            goto Lnomatch;
                        }
                        if (!(*parameters)[j].matchArg(sc, e1, j, parameters, dedtypes, null))
                            goto Lnomatch;
                    }
                    else if (s1 && s2)
                    {
                    Ls:
                        if (!s1.equals(s2))
                            goto Lnomatch;
                    }
                    else if (s1 && t2 && t2.ty == Tident)
                    {
                        j = templateParameterLookup(t2, parameters);
                        if (j == IDX_NOTFOUND)
                        {
                            t2.resolve((cast(TypeIdentifier)t2).loc, sc, &e2, &t2, &s2);
                            if (s2)
                                goto Ls;
                            goto Lnomatch;
                        }
                        if (!(*parameters)[j].matchArg(sc, s1, j, parameters, dedtypes, null))
                            goto Lnomatch;
                    }
                    else
                        goto Lnomatch;
                }
            }
            visit(cast(Type)t);
            return;

        Lnomatch:
            //printf("no match\n");
            result = MATCHnomatch;
        }

        override void visit(TypeStruct t)
        {
            version (none)
            {
                printf("TypeStruct.deduceType()\n");
                printf("\tthis.parent   = %s, ", t.sym.parent.toChars());
                t.print();
                printf("\ttparam = %d, ", tparam.ty);
                tparam.print();
            }

            /* If this struct is a template struct, and we're matching
             * it against a template instance, convert the struct type
             * to a template instance, too, and try again.
             */
            TemplateInstance ti = t.sym.parent.isTemplateInstance();

            if (tparam && tparam.ty == Tinstance)
            {
                if (ti && ti.toAlias() == t.sym)
                {
                    auto tx = new TypeInstance(Loc(), ti);
                    result = deduceType(tx, sc, tparam, parameters, dedtypes, wm);
                    return;
                }

                /* Match things like:
                 *  S!(T).foo
                 */
                TypeInstance tpi = cast(TypeInstance)tparam;
                if (tpi.idents.dim)
                {
                    RootObject id = tpi.idents[tpi.idents.dim - 1];
                    if (id.dyncast() == DYNCAST.identifier && t.sym.ident.equals(cast(Identifier)id))
                    {
                        Type tparent = t.sym.parent.getType();
                        if (tparent)
                        {
                            /* Slice off the .foo in S!(T).foo
                             */
                            tpi.idents.dim--;
                            result = deduceType(tparent, sc, tpi, parameters, dedtypes, wm);
                            tpi.idents.dim++;
                            return;
                        }
                    }
                }
            }

            // Extra check
            if (tparam && tparam.ty == Tstruct)
            {
                TypeStruct tp = cast(TypeStruct)tparam;

                //printf("\t%d\n", (MATCH) t.implicitConvTo(tp));
                if (wm && t.deduceWild(tparam, false))
                {
                    result = MATCHconst;
                    return;
                }
                result = t.implicitConvTo(tp);
                return;
            }
            visit(cast(Type)t);
        }

        override void visit(TypeEnum t)
        {
            // Extra check
            if (tparam && tparam.ty == Tenum)
            {
                TypeEnum tp = cast(TypeEnum)tparam;
                if (t.sym == tp.sym)
                    visit(cast(Type)t);
                else
                    result = MATCHnomatch;
                return;
            }
            Type tb = t.toBasetype();
            if (tb.ty == tparam.ty || tb.ty == Tsarray && tparam.ty == Taarray)
            {
                result = deduceType(tb, sc, tparam, parameters, dedtypes, wm);
                return;
            }
            visit(cast(Type)t);
        }

        /* Helper for TypeClass.deduceType().
         * Classes can match with implicit conversion to a base class or interface.
         * This is complicated, because there may be more than one base class which
         * matches. In such cases, one or more parameters remain ambiguous.
         * For example,
         *
         *   interface I(X, Y) {}
         *   class C : I(uint, double), I(char, double) {}
         *   C x;
         *   foo(T, U)( I!(T, U) x)
         *
         *   deduces that U is double, but T remains ambiguous (could be char or uint).
         *
         * Given a baseclass b, and initial deduced types 'dedtypes', this function
         * tries to match tparam with b, and also tries all base interfaces of b.
         * If a match occurs, numBaseClassMatches is incremented, and the new deduced
         * types are ANDed with the current 'best' estimate for dedtypes.
         */
        static void deduceBaseClassParameters(ref BaseClass b, Scope* sc, Type tparam, TemplateParameters* parameters, Objects* dedtypes, Objects* best, ref int numBaseClassMatches)
        {
            TemplateInstance parti = b.sym ? b.sym.parent.isTemplateInstance() : null;
            if (parti)
            {
                // Make a temporary copy of dedtypes so we don't destroy it
                auto tmpdedtypes = new Objects();
                tmpdedtypes.setDim(dedtypes.dim);
                memcpy(tmpdedtypes.tdata(), dedtypes.tdata(), dedtypes.dim * (void*).sizeof);

                auto t = new TypeInstance(Loc(), parti);
                MATCH m = deduceType(t, sc, tparam, parameters, tmpdedtypes);
                if (m > MATCHnomatch)
                {
                    // If this is the first ever match, it becomes our best estimate
                    if (numBaseClassMatches == 0)
                        memcpy(best.tdata(), tmpdedtypes.tdata(), tmpdedtypes.dim * (void*).sizeof);
                    else
                        for (size_t k = 0; k < tmpdedtypes.dim; ++k)
                        {
                            // If we've found more than one possible type for a parameter,
                            // mark it as unknown.
                            if ((*tmpdedtypes)[k] != (*best)[k])
                                (*best)[k] = (*dedtypes)[k];
                        }
                    ++numBaseClassMatches;
                }
            }

            // Now recursively test the inherited interfaces
            foreach (ref bi; b.baseInterfaces)
            {
                deduceBaseClassParameters(bi, sc, tparam, parameters, dedtypes, best, numBaseClassMatches);
            }
        }

        override void visit(TypeClass t)
        {
            //printf("TypeClass.deduceType(this = %s)\n", t.toChars());

            /* If this class is a template class, and we're matching
             * it against a template instance, convert the class type
             * to a template instance, too, and try again.
             */
            TemplateInstance ti = t.sym.parent.isTemplateInstance();

            if (tparam && tparam.ty == Tinstance)
            {
                if (ti && ti.toAlias() == t.sym)
                {
                    auto tx = new TypeInstance(Loc(), ti);
                    MATCH m = deduceType(tx, sc, tparam, parameters, dedtypes, wm);
                    // Even if the match fails, there is still a chance it could match
                    // a base class.
                    if (m != MATCHnomatch)
                    {
                        result = m;
                        return;
                    }
                }

                /* Match things like:
                 *  S!(T).foo
                 */
                TypeInstance tpi = cast(TypeInstance)tparam;
                if (tpi.idents.dim)
                {
                    RootObject id = tpi.idents[tpi.idents.dim - 1];
                    if (id.dyncast() == DYNCAST.identifier && t.sym.ident.equals(cast(Identifier)id))
                    {
                        Type tparent = t.sym.parent.getType();
                        if (tparent)
                        {
                            /* Slice off the .foo in S!(T).foo
                             */
                            tpi.idents.dim--;
                            result = deduceType(tparent, sc, tpi, parameters, dedtypes, wm);
                            tpi.idents.dim++;
                            return;
                        }
                    }
                }

                // If it matches exactly or via implicit conversion, we're done
                visit(cast(Type)t);
                if (result != MATCHnomatch)
                    return;

                /* There is still a chance to match via implicit conversion to
                 * a base class or interface. Because there could be more than one such
                 * match, we need to check them all.
                 */

                int numBaseClassMatches = 0; // Have we found an interface match?

                // Our best guess at dedtypes
                auto best = new Objects();
                best.setDim(dedtypes.dim);

                ClassDeclaration s = t.sym;
                while (s && s.baseclasses.dim > 0)
                {
                    // Test the base class
                    deduceBaseClassParameters(*(*s.baseclasses)[0], sc, tparam, parameters, dedtypes, best, numBaseClassMatches);

                    // Test the interfaces inherited by the base class
                    foreach (b; s.interfaces)
                    {
                        deduceBaseClassParameters(*b, sc, tparam, parameters, dedtypes, best, numBaseClassMatches);
                    }
                    s = (*s.baseclasses)[0].sym;
                }

                if (numBaseClassMatches == 0)
                {
                    result = MATCHnomatch;
                    return;
                }

                // If we got at least one match, copy the known types into dedtypes
                memcpy(dedtypes.tdata(), best.tdata(), best.dim * (void*).sizeof);
                result = MATCHconvert;
                return;
            }

            // Extra check
            if (tparam && tparam.ty == Tclass)
            {
                TypeClass tp = cast(TypeClass)tparam;

                //printf("\t%d\n", (MATCH) t.implicitConvTo(tp));
                if (wm && t.deduceWild(tparam, false))
                {
                    result = MATCHconst;
                    return;
                }
                result = t.implicitConvTo(tp);
                return;
            }
            visit(cast(Type)t);
        }

        override void visit(Expression e)
        {
            //printf("Expression.deduceType(e = %s)\n", e.toChars());
            size_t i = templateParameterLookup(tparam, parameters);
            if (i == IDX_NOTFOUND || (cast(TypeIdentifier)tparam).idents.dim > 0)
            {
                if (e == emptyArrayElement && tparam.ty == Tarray)
                {
                    Type tn = (cast(TypeNext)tparam).next;
                    result = deduceType(emptyArrayElement, sc, tn, parameters, dedtypes, wm);
                    return;
                }
                e.type.accept(this);
                return;
            }

            TemplateTypeParameter tp = (*parameters)[i].isTemplateTypeParameter();
            if (!tp)
                return; // nomatch

            if (e == emptyArrayElement)
            {
                if ((*dedtypes)[i])
                {
                    result = MATCHexact;
                    return;
                }
                if (tp.defaultType)
                {
                    tp.defaultType.accept(this);
                    return;
                }
            }

            Type at = cast(Type)(*dedtypes)[i];
            Type tt;
            if (ubyte wx = deduceWildHelper(e.type, &tt, tparam))
            {
                *wm |= wx;
                result = MATCHconst;
            }
            else if (MATCH m = deduceTypeHelper(e.type, &tt, tparam))
            {
                result = m;
            }
            else
                return; // nomatch

            // expression vs (none)
            if (!at)
            {
                (*dedtypes)[i] = new TypeDeduced(tt, e, tparam);
                return;
            }

            TypeDeduced xt = null;
            if (at.ty == Tnone)
            {
                xt = cast(TypeDeduced)at;
                at = xt.tded;
            }

            // From previous matched expressions to current deduced type
            MATCH match1 = xt ? xt.matchAll(tt) : MATCHnomatch;

            // From current expresssion to previous deduced type
            Type pt = at.addMod(tparam.mod);
            if (*wm)
                pt = pt.substWildTo(*wm);
            MATCH match2 = e.implicitConvTo(pt);

            if (match1 > MATCHnomatch && match2 > MATCHnomatch)
            {
                if (at.implicitConvTo(tt) <= MATCHnomatch)
                    match1 = MATCHnomatch; // Prefer at
                else if (tt.implicitConvTo(at) <= MATCHnomatch)
                    match2 = MATCHnomatch; // Prefer tt
                else if (tt.isTypeBasic() && tt.ty == at.ty && tt.mod != at.mod)
                {
                    if (!tt.isMutable() && !at.isMutable())
                        tt = tt.mutableOf().addMod(MODmerge(tt.mod, at.mod));
                    else if (tt.isMutable())
                    {
                        if (at.mod == 0) // Prefer unshared
                            match1 = MATCHnomatch;
                        else
                            match2 = MATCHnomatch;
                    }
                    else if (at.isMutable())
                    {
                        if (tt.mod == 0) // Prefer unshared
                            match2 = MATCHnomatch;
                        else
                            match1 = MATCHnomatch;
                    }
                    //printf("tt = %s, at = %s\n", tt.toChars(), at.toChars());
                }
                else
                {
                    match1 = MATCHnomatch;
                    match2 = MATCHnomatch;
                }
            }
            if (match1 > MATCHnomatch)
            {
                // Prefer current match: tt
                if (xt)
                    xt.update(tt, e, tparam);
                else
                    (*dedtypes)[i] = tt;
                result = match1;
                return;
            }
            if (match2 > MATCHnomatch)
            {
                // Prefer previous match: (*dedtypes)[i]
                if (xt)
                    xt.update(e, tparam);
                result = match2;
                return;
            }

            /* Deduce common type
             */
            if (Type t = rawTypeMerge(at, tt))
            {
                if (xt)
                    xt.update(t, e, tparam);
                else
                    (*dedtypes)[i] = t;

                pt = tt.addMod(tparam.mod);
                if (*wm)
                    pt = pt.substWildTo(*wm);
                result = e.implicitConvTo(pt);
                return;
            }

            result = MATCHnomatch;
        }

        MATCH deduceEmptyArrayElement()
        {
            if (!emptyArrayElement)
            {
                emptyArrayElement = new IdentifierExp(Loc(), Id.p); // dummy
                emptyArrayElement.type = Type.tvoid;
            }
            assert(tparam.ty == Tarray);

            Type tn = (cast(TypeNext)tparam).next;
            return deduceType(emptyArrayElement, sc, tn, parameters, dedtypes, wm);
        }

        override void visit(NullExp e)
        {
            if (tparam.ty == Tarray && e.type.ty == Tnull)
            {
                // tparam:T[] <- e:null (void[])
                result = deduceEmptyArrayElement();
                return;
            }
            visit(cast(Expression)e);
        }

        override void visit(StringExp e)
        {
            Type taai;
            if (e.type.ty == Tarray && (tparam.ty == Tsarray || tparam.ty == Taarray && (taai = (cast(TypeAArray)tparam).index).ty == Tident && (cast(TypeIdentifier)taai).idents.dim == 0))
            {
                // Consider compile-time known boundaries
                e.type.nextOf().sarrayOf(e.len).accept(this);
                return;
            }
            visit(cast(Expression)e);
        }

        override void visit(ArrayLiteralExp e)
        {
            if ((!e.elements || !e.elements.dim) && e.type.toBasetype().nextOf().ty == Tvoid && tparam.ty == Tarray)
            {
                // tparam:T[] <- e:[] (void[])
                result = deduceEmptyArrayElement();
                return;
            }

            if (tparam.ty == Tarray && e.elements && e.elements.dim)
            {
                Type tn = (cast(TypeDArray)tparam).next;
                result = MATCHexact;
                if (e.basis)
                {
                    MATCH m = deduceType(e.basis, sc, tn, parameters, dedtypes, wm);
                    if (m < result)
                        result = m;
                }
                for (size_t i = 0; i < e.elements.dim; i++)
                {
                    if (result <= MATCHnomatch)
                        break;
                    auto el = (*e.elements)[i];
                    if (!el)
                        continue;
                    MATCH m = deduceType(el, sc, tn, parameters, dedtypes, wm);
                    if (m < result)
                        result = m;
                }
                return;
            }

            Type taai;
            if (e.type.ty == Tarray && (tparam.ty == Tsarray || tparam.ty == Taarray && (taai = (cast(TypeAArray)tparam).index).ty == Tident && (cast(TypeIdentifier)taai).idents.dim == 0))
            {
                // Consider compile-time known boundaries
                e.type.nextOf().sarrayOf(e.elements.dim).accept(this);
                return;
            }
            visit(cast(Expression)e);
        }

        override void visit(AssocArrayLiteralExp e)
        {
            if (tparam.ty == Taarray && e.keys && e.keys.dim)
            {
                TypeAArray taa = cast(TypeAArray)tparam;
                result = MATCHexact;
                for (size_t i = 0; i < e.keys.dim; i++)
                {
                    MATCH m1 = deduceType((*e.keys)[i], sc, taa.index, parameters, dedtypes, wm);
                    if (m1 < result)
                        result = m1;
                    if (result <= MATCHnomatch)
                        break;
                    MATCH m2 = deduceType((*e.values)[i], sc, taa.next, parameters, dedtypes, wm);
                    if (m2 < result)
                        result = m2;
                    if (result <= MATCHnomatch)
                        break;
                }
                return;
            }
            visit(cast(Expression)e);
        }

        override void visit(FuncExp e)
        {
            //printf("e.type = %s, tparam = %s\n", e.type.toChars(), tparam.toChars());
            if (e.td)
            {
                Type to = tparam;
                if (!to.nextOf() || to.nextOf().ty != Tfunction)
                    return;
                TypeFunction tof = cast(TypeFunction)to.nextOf();

                // Parameter types inference from 'tof'
                assert(e.td._scope);
                TypeFunction tf = cast(TypeFunction)e.fd.type;
                //printf("\ttof = %s\n", tof.toChars());
                //printf("\ttf  = %s\n", tf.toChars());
                size_t dim = Parameter.dim(tf.parameters);

                if (Parameter.dim(tof.parameters) != dim || tof.varargs != tf.varargs)
                    return;

                auto tiargs = new Objects();
                tiargs.reserve(e.td.parameters.dim);

                for (size_t i = 0; i < e.td.parameters.dim; i++)
                {
                    TemplateParameter tp = (*e.td.parameters)[i];
                    size_t u = 0;
                    for (; u < dim; u++)
                    {
                        Parameter p = Parameter.getNth(tf.parameters, u);
                        if (p.type.ty == Tident && (cast(TypeIdentifier)p.type).ident == tp.ident)
                        {
                            break;
                        }
                    }
                    assert(u < dim);
                    Parameter pto = Parameter.getNth(tof.parameters, u);
                    if (!pto)
                        break;
                    Type t = pto.type.syntaxCopy(); // https://issues.dlang.org/show_bug.cgi?id=11774
                    if (reliesOnTident(t, parameters, inferStart))
                        return;
                    t = t.semantic(e.loc, sc);
                    if (t.ty == Terror)
                        return;
                    tiargs.push(t);
                }

                // Set target of return type inference
                if (!tf.next && tof.next)
                    e.fd.treq = tparam;

                auto ti = new TemplateInstance(e.loc, e.td, tiargs);
                Expression ex = (new ScopeExp(e.loc, ti)).semantic(e.td._scope);

                // Reset inference target for the later re-semantic
                e.fd.treq = null;

                if (ex.op == TOKerror)
                    return;
                if (ex.op != TOKfunction)
                    return;
                visit(ex.type);
                return;
            }

            Type t = e.type;

            if (t.ty == Tdelegate && tparam.ty == Tpointer)
                return;

            // Allow conversion from implicit function pointer to delegate
            if (e.tok == TOKreserved && t.ty == Tpointer && tparam.ty == Tdelegate)
            {
                TypeFunction tf = cast(TypeFunction)t.nextOf();
                t = (new TypeDelegate(tf)).merge();
            }
            //printf("tparam = %s <= e.type = %s, t = %s\n", tparam.toChars(), e.type.toChars(), t.toChars());
            visit(t);
        }

        override void visit(SliceExp e)
        {
            Type taai;
            if (e.type.ty == Tarray && (tparam.ty == Tsarray || tparam.ty == Taarray && (taai = (cast(TypeAArray)tparam).index).ty == Tident && (cast(TypeIdentifier)taai).idents.dim == 0))
            {
                // Consider compile-time known boundaries
                if (Type tsa = toStaticArrayType(e))
                {
                    tsa.accept(this);
                    return;
                }
            }
            visit(cast(Expression)e);
        }

        override void visit(CommaExp e)
        {
            e.e2.accept(this);
        }
    }

    scope DeduceType v = new DeduceType(sc, tparam, parameters, dedtypes, wm, inferStart);
    if (Type t = isType(o))
        t.accept(v);
    else
    {
        assert(isExpression(o) && wm);
        (cast(Expression)o).accept(v);
    }
    return v.result;
}

/***********************************************************
 * Check whether the type t representation relies on one or more the template parameters.
 * Params:
 *      t           = Tested type, if null, returns false.
 *      tparams     = Template parameters.
 *      iStart      = Start index of tparams to limit the tested parameters. If it's
 *                    nonzero, tparams[0..iStart] will be excluded from the test target.
 */
private bool reliesOnTident(Type t, TemplateParameters* tparams = null, size_t iStart = 0)
{
    extern (C++) final class ReliesOnTident : Visitor
    {
        alias visit = super.visit;
    public:
        TemplateParameters* tparams;
        size_t iStart;
        bool result;

        extern (D) this(TemplateParameters* tparams, size_t iStart)
        {
            this.tparams = tparams;
            this.iStart = iStart;
        }

        override void visit(Type t)
        {
        }

        override void visit(TypeNext t)
        {
            t.next.accept(this);
        }

        override void visit(TypeVector t)
        {
            t.basetype.accept(this);
        }

        override void visit(TypeAArray t)
        {
            visit(cast(TypeNext)t);
            if (!result)
                t.index.accept(this);
        }

        override void visit(TypeFunction t)
        {
            size_t dim = Parameter.dim(t.parameters);
            for (size_t i = 0; i < dim; i++)
            {
                Parameter fparam = Parameter.getNth(t.parameters, i);
                fparam.type.accept(this);
                if (result)
                    return;
            }
            if (t.next)
                t.next.accept(this);
        }

        override void visit(TypeIdentifier t)
        {
            for (size_t i = iStart; i < tparams.dim; i++)
            {
                TemplateParameter tp = (*tparams)[i];
                if (tp.ident.equals(t.ident))
                {
                    result = true;
                    return;
                }
            }
        }

        override void visit(TypeInstance t)
        {
            for (size_t i = iStart; i < tparams.dim; i++)
            {
                TemplateParameter tp = (*tparams)[i];
                if (t.tempinst.name == tp.ident)
                {
                    result = true;
                    return;
                }
            }
            if (!t.tempinst.tiargs)
                return;
            for (size_t i = 0; i < t.tempinst.tiargs.dim; i++)
            {
                Type ta = isType((*t.tempinst.tiargs)[i]);
                if (ta)
                {
                    ta.accept(this);
                    if (result)
                        return;
                }
            }
        }

        override void visit(TypeTypeof t)
        {
            //printf("TypeTypeof.reliesOnTident('%s')\n", t.toChars());
            t.exp.accept(this);
        }

        override void visit(TypeTuple t)
        {
            if (t.arguments)
            {
                for (size_t i = 0; i < t.arguments.dim; i++)
                {
                    Parameter arg = (*t.arguments)[i];
                    arg.type.accept(this);
                    if (result)
                        return;
                }
            }
        }

        override void visit(Expression e)
        {
            //printf("Expression.reliesOnTident('%s')\n", e.toChars());
        }

        override void visit(IdentifierExp e)
        {
            //printf("IdentifierExp.reliesOnTident('%s')\n", e.toChars());
            for (size_t i = iStart; i < tparams.dim; i++)
            {
                auto tp = (*tparams)[i];
                if (e.ident == tp.ident)
                {
                    result = true;
                    return;
                }
            }
        }

        override void visit(TupleExp e)
        {
            //printf("TupleExp.reliesOnTident('%s')\n", e.toChars());
            if (e.exps)
            {
                foreach (ea; *e.exps)
                {
                    ea.accept(this);
                    if (result)
                        return;
                }
            }
        }

        override void visit(ArrayLiteralExp e)
        {
            //printf("ArrayLiteralExp.reliesOnTident('%s')\n", e.toChars());
            if (e.elements)
            {
                foreach (el; *e.elements)
                {
                    el.accept(this);
                    if (result)
                        return;
                }
            }
        }

        override void visit(AssocArrayLiteralExp e)
        {
            //printf("AssocArrayLiteralExp.reliesOnTident('%s')\n", e.toChars());
            foreach (ek; *e.keys)
            {
                ek.accept(this);
                if (result)
                    return;
            }
            foreach (ev; *e.values)
            {
                ev.accept(this);
                if (result)
                    return;
            }
        }

        override void visit(StructLiteralExp e)
        {
            //printf("StructLiteralExp.reliesOnTident('%s')\n", e.toChars());
            if (e.elements)
            {
                foreach (ea; *e.elements)
                {
                    ea.accept(this);
                    if (result)
                        return;
                }
            }
        }

        override void visit(TypeExp e)
        {
            //printf("TypeExp.reliesOnTident('%s')\n", e.toChars());
            e.type.accept(this);
        }

        override void visit(NewExp e)
        {
            //printf("NewExp.reliesOnTident('%s')\n", e.toChars());
            if (e.thisexp)
                e.thisexp.accept(this);
            if (!result && e.newargs)
            {
                foreach (ea; *e.newargs)
                {
                    ea.accept(this);
                    if (result)
                        return;
                }
            }
            e.newtype.accept(this);
            if (!result && e.arguments)
            {
                foreach (ea; *e.arguments)
                {
                    ea.accept(this);
                    if (result)
                        return;
                }
            }
        }

        override void visit(NewAnonClassExp e)
        {
            //printf("NewAnonClassExp.reliesOnTident('%s')\n", e.toChars());
            result = true;
        }

        override void visit(FuncExp e)
        {
            //printf("FuncExp.reliesOnTident('%s')\n", e.toChars());
            result = true;
        }

        override void visit(TypeidExp e)
        {
            //printf("TypeidExp.reliesOnTident('%s')\n", e.toChars());
            if (auto ea = isExpression(e.obj))
                ea.accept(this);
            else if (auto ta = isType(e.obj))
                ta.accept(this);
        }

        override void visit(TraitsExp e)
        {
            //printf("TraitsExp.reliesOnTident('%s')\n", e.toChars());
            if (e.args)
            {
                foreach (oa; *e.args)
                {
                    if (auto ea = isExpression(oa))
                        ea.accept(this);
                    else if (auto ta = isType(oa))
                        ta.accept(this);
                    if (result)
                        return;
                }
            }
        }

        override void visit(IsExp e)
        {
            //printf("IsExp.reliesOnTident('%s')\n", e.toChars());
            e.targ.accept(this);
        }

        override void visit(UnaExp e)
        {
            //printf("UnaExp.reliesOnTident('%s')\n", e.toChars());
            e.e1.accept(this);
        }

        override void visit(DotTemplateInstanceExp e)
        {
            //printf("DotTemplateInstanceExp.reliesOnTident('%s')\n", e.toChars());
            visit(cast(UnaExp)e);
            if (!result && e.ti.tiargs)
            {
                foreach (oa; *e.ti.tiargs)
                {
                    if (auto ea = isExpression(oa))
                        ea.accept(this);
                    else if (auto ta = isType(oa))
                        ta.accept(this);
                    if (result)
                        return;
                }
            }
        }

        override void visit(CallExp e)
        {
            //printf("CallExp.reliesOnTident('%s')\n", e.toChars());
            visit(cast(UnaExp)e);
            if (!result && e.arguments)
            {
                foreach (ea; *e.arguments)
                {
                    ea.accept(this);
                    if (result)
                        return;
                }
            }
        }

        override void visit(CastExp e)
        {
            //printf("CallExp.reliesOnTident('%s')\n", e.toChars());
            visit(cast(UnaExp)e);
            if (!result)
                e.to.accept(this);
        }

        override void visit(SliceExp e)
        {
            //printf("SliceExp.reliesOnTident('%s')\n", e.toChars());
            visit(cast(UnaExp)e);
            if (!result && e.lwr)
                e.lwr.accept(this);
            if (!result && e.upr)
                e.upr.accept(this);
        }

        override void visit(IntervalExp e)
        {
            //printf("IntervalExp.reliesOnTident('%s')\n", e.toChars());
            e.lwr.accept(this);
            if (!result)
                e.upr.accept(this);
        }

        override void visit(ArrayExp e)
        {
            //printf("ArrayExp.reliesOnTident('%s')\n", e.toChars());
            visit(cast(UnaExp)e);
            if (!result && e.arguments)
            {
                foreach (ea; *e.arguments)
                    ea.accept(this);
            }
        }

        override void visit(BinExp e)
        {
            //printf("BinExp.reliesOnTident('%s')\n", e.toChars());
            e.e1.accept(this);
            if (!result)
                e.e2.accept(this);
        }

        override void visit(CondExp e)
        {
            //printf("BinExp.reliesOnTident('%s')\n", e.toChars());
            e.econd.accept(this);
            if (!result)
                visit(cast(BinExp)e);
        }
    }

    if (!t)
        return false;

    assert(tparams);
    scope ReliesOnTident v = new ReliesOnTident(tparams, iStart);
    t.accept(v);
    return v.result;
}

/***********************************************************
 */
extern (C++) class TemplateParameter
{
    Loc loc;
    Identifier ident;

    /* True if this is a part of precedent parameter specialization pattern.
     *
     *  template A(T : X!TL, alias X, TL...) {}
     *  // X and TL are dependent template parameter
     *
     * A dependent template parameter should return MATCHexact in matchArg()
     * to respect the match level of the corresponding precedent parameter.
     */
    bool dependent;

    /* ======================== TemplateParameter =============================== */
    final extern (D) this(Loc loc, Identifier ident)
    {
        this.loc = loc;
        this.ident = ident;
    }

    TemplateTypeParameter isTemplateTypeParameter()
    {
        return null;
    }

    TemplateValueParameter isTemplateValueParameter()
    {
        return null;
    }

    TemplateAliasParameter isTemplateAliasParameter()
    {
        return null;
    }

    TemplateThisParameter isTemplateThisParameter()
    {
        return null;
    }

    TemplateTupleParameter isTemplateTupleParameter()
    {
        return null;
    }

    abstract TemplateParameter syntaxCopy();

    abstract bool declareParameter(Scope* sc);

    abstract bool semantic(Scope* sc, TemplateParameters* parameters);

    abstract void print(RootObject oarg, RootObject oded);

    abstract RootObject specialization();

    abstract RootObject defaultArg(Loc instLoc, Scope* sc);

    abstract bool hasDefaultArg();

    /*******************************************
     * Match to a particular TemplateParameter.
     * Input:
     *      instLoc         location that the template is instantiated.
     *      tiargs[]        actual arguments to template instance
     *      i               i'th argument
     *      parameters[]    template parameters
     *      dedtypes[]      deduced arguments to template instance
     *      *psparam        set to symbol declared and initialized to dedtypes[i]
     */
    MATCH matchArg(Loc instLoc, Scope* sc, Objects* tiargs, size_t i, TemplateParameters* parameters, Objects* dedtypes, Declaration* psparam)
    {
        RootObject oarg;

        if (i < tiargs.dim)
            oarg = (*tiargs)[i];
        else
        {
            // Get default argument instead
            oarg = defaultArg(instLoc, sc);
            if (!oarg)
            {
                assert(i < dedtypes.dim);
                // It might have already been deduced
                oarg = (*dedtypes)[i];
                if (!oarg)
                    goto Lnomatch;
            }
        }
        return matchArg(sc, oarg, i, parameters, dedtypes, psparam);

    Lnomatch:
        if (psparam)
            *psparam = null;
        return MATCHnomatch;
    }

    abstract MATCH matchArg(Scope* sc, RootObject oarg, size_t i, TemplateParameters* parameters, Objects* dedtypes, Declaration* psparam);

    /* Create dummy argument based on parameter.
     */
    abstract void* dummyArg();

    void accept(Visitor v)
    {
        v.visit(this);
    }
}

/***********************************************************
 * Syntax:
 *  ident : specType = defaultType
 */
extern (C++) class TemplateTypeParameter : TemplateParameter
{
    Type specType;      // if !=null, this is the type specialization
    Type defaultType;

    extern (C++) static __gshared Type tdummy = null;

    final extern (D) this(Loc loc, Identifier ident, Type specType, Type defaultType)
    {
        super(loc, ident);
        this.ident = ident;
        this.specType = specType;
        this.defaultType = defaultType;
    }

    override final TemplateTypeParameter isTemplateTypeParameter()
    {
        return this;
    }

    override TemplateParameter syntaxCopy()
    {
        return new TemplateTypeParameter(loc, ident, specType ? specType.syntaxCopy() : null, defaultType ? defaultType.syntaxCopy() : null);
    }

    override final bool declareParameter(Scope* sc)
    {
        //printf("TemplateTypeParameter.declareParameter('%s')\n", ident.toChars());
        auto ti = new TypeIdentifier(loc, ident);
        Declaration ad = new AliasDeclaration(loc, ident, ti);
        return sc.insert(ad) !is null;
    }

    override final bool semantic(Scope* sc, TemplateParameters* parameters)
    {
        //printf("TemplateTypeParameter.semantic('%s')\n", ident.toChars());
        if (specType && !reliesOnTident(specType, parameters))
        {
            specType = specType.semantic(loc, sc);
        }
        version (none)
        {
            // Don't do semantic() until instantiation
            if (defaultType)
            {
                defaultType = defaultType.semantic(loc, sc);
            }
        }
        return !(specType && isError(specType));
    }

    override final void print(RootObject oarg, RootObject oded)
    {
        printf(" %s\n", ident.toChars());

        Type t = isType(oarg);
        Type ta = isType(oded);
        assert(ta);

        if (specType)
            printf("\tSpecialization: %s\n", specType.toChars());
        if (defaultType)
            printf("\tDefault:        %s\n", defaultType.toChars());
        printf("\tParameter:       %s\n", t ? t.toChars() : "NULL");
        printf("\tDeduced Type:   %s\n", ta.toChars());
    }

    override final RootObject specialization()
    {
        return specType;
    }

    override final RootObject defaultArg(Loc instLoc, Scope* sc)
    {
        Type t = defaultType;
        if (t)
        {
            t = t.syntaxCopy();
            t = t.semantic(loc, sc); // use the parameter loc
        }
        return t;
    }

    override final bool hasDefaultArg()
    {
        return defaultType !is null;
    }

    override final MATCH matchArg(Scope* sc, RootObject oarg, size_t i, TemplateParameters* parameters, Objects* dedtypes, Declaration* psparam)
    {
        //printf("TemplateTypeParameter.matchArg('%s')\n", ident.toChars());
        MATCH m = MATCHexact;
        Type ta = isType(oarg);
        if (!ta)
        {
            //printf("%s %p %p %p\n", oarg.toChars(), isExpression(oarg), isDsymbol(oarg), isTuple(oarg));
            goto Lnomatch;
        }
        //printf("ta is %s\n", ta.toChars());

        if (specType)
        {
            if (!ta || ta == tdummy)
                goto Lnomatch;

            //printf("\tcalling deduceType(): ta is %s, specType is %s\n", ta.toChars(), specType.toChars());
            MATCH m2 = deduceType(ta, sc, specType, parameters, dedtypes);
            if (m2 <= MATCHnomatch)
            {
                //printf("\tfailed deduceType\n");
                goto Lnomatch;
            }

            if (m2 < m)
                m = m2;
            if ((*dedtypes)[i])
            {
                Type t = cast(Type)(*dedtypes)[i];

                if (dependent && !t.equals(ta)) // https://issues.dlang.org/show_bug.cgi?id=14357
                    goto Lnomatch;

                /* This is a self-dependent parameter. For example:
                 *  template X(T : T*) {}
                 *  template X(T : S!T, alias S) {}
                 */
                //printf("t = %s ta = %s\n", t.toChars(), ta.toChars());
                ta = t;
            }
        }
        else
        {
            if ((*dedtypes)[i])
            {
                // Must match already deduced type
                Type t = cast(Type)(*dedtypes)[i];

                if (!t.equals(ta))
                {
                    //printf("t = %s ta = %s\n", t.toChars(), ta.toChars());
                    goto Lnomatch;
                }
            }
            else
            {
                // So that matches with specializations are better
                m = MATCHconvert;
            }
        }
        (*dedtypes)[i] = ta;

        if (psparam)
            *psparam = new AliasDeclaration(loc, ident, ta);
        //printf("\tm = %d\n", m);
        return dependent ? MATCHexact : m;

    Lnomatch:
        if (psparam)
            *psparam = null;
        //printf("\tm = %d\n", MATCHnomatch);
        return MATCHnomatch;
    }

    override final void* dummyArg()
    {
        Type t = specType;
        if (!t)
        {
            // Use this for alias-parameter's too (?)
            if (!tdummy)
                tdummy = new TypeIdentifier(loc, ident);
            t = tdummy;
        }
        return cast(void*)t;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/***********************************************************
 * Syntax:
 *  this ident : specType = defaultType
 */
extern (C++) final class TemplateThisParameter : TemplateTypeParameter
{
    extern (D) this(Loc loc, Identifier ident, Type specType, Type defaultType)
    {
        super(loc, ident, specType, defaultType);
    }

    override TemplateThisParameter isTemplateThisParameter()
    {
        return this;
    }

    override TemplateParameter syntaxCopy()
    {
        return new TemplateThisParameter(loc, ident, specType ? specType.syntaxCopy() : null, defaultType ? defaultType.syntaxCopy() : null);
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/***********************************************************
 * Syntax:
 *  valType ident : specValue = defaultValue
 */
extern (C++) final class TemplateValueParameter : TemplateParameter
{
    Type valType;
    Expression specValue;
    Expression defaultValue;

    extern (C++) static __gshared AA* edummies = null;

    extern (D) this(Loc loc, Identifier ident, Type valType,
        Expression specValue, Expression defaultValue)
    {
        super(loc, ident);
        this.ident = ident;
        this.valType = valType;
        this.specValue = specValue;
        this.defaultValue = defaultValue;
    }

    override TemplateValueParameter isTemplateValueParameter()
    {
        return this;
    }

    override TemplateParameter syntaxCopy()
    {
        return new TemplateValueParameter(loc, ident,
            valType.syntaxCopy(),
            specValue ? specValue.syntaxCopy() : null,
            defaultValue ? defaultValue.syntaxCopy() : null);
    }

    override bool declareParameter(Scope* sc)
    {
        auto v = new VarDeclaration(loc, valType, ident, null);
        v.storage_class = STCtemplateparameter;
        return sc.insert(v) !is null;
    }

    override bool semantic(Scope* sc, TemplateParameters* parameters)
    {
        valType = valType.semantic(loc, sc);
        version (none)
        {
            // defer semantic analysis to arg match
            if (specValue)
            {
                Expression e = specValue;
                sc = sc.startCTFE();
                e = e.semantic(sc);
                sc = sc.endCTFE();
                e = e.implicitCastTo(sc, valType);
                e = e.ctfeInterpret();
                if (e.op == TOKint64 || e.op == TOKfloat64 ||
                    e.op == TOKcomplex80 || e.op == TOKnull || e.op == TOKstring)
                    specValue = e;
            }

            if (defaultValue)
            {
                Expression e = defaultValue;
                sc = sc.startCTFE();
                e = e.semantic(sc);
                sc = sc.endCTFE();
                e = e.implicitCastTo(sc, valType);
                e = e.ctfeInterpret();
                if (e.op == TOKint64)
                    defaultValue = e;
            }
        }
        return !isError(valType);
    }

    override void print(RootObject oarg, RootObject oded)
    {
        printf(" %s\n", ident.toChars());
        Expression ea = isExpression(oded);
        if (specValue)
            printf("\tSpecialization: %s\n", specValue.toChars());
        printf("\tParameter Value: %s\n", ea ? ea.toChars() : "NULL");
    }

    override RootObject specialization()
    {
        return specValue;
    }

    override RootObject defaultArg(Loc instLoc, Scope* sc)
    {
        Expression e = defaultValue;
        if (e)
        {
            e = e.syntaxCopy();
            if ((e = e.semantic(sc)) is null)
                return null;
            if ((e = resolveProperties(sc, e)) is null)
                return null;
            e = e.resolveLoc(instLoc, sc); // use the instantiated loc
            e = e.optimize(WANTvalue);
        }
        return e;
    }

    override bool hasDefaultArg()
    {
        return defaultValue !is null;
    }

    override MATCH matchArg(Scope* sc, RootObject oarg,
        size_t i, TemplateParameters* parameters, Objects* dedtypes,
        Declaration* psparam)
    {
        //printf("TemplateValueParameter.matchArg('%s')\n", ident.toChars());

        MATCH m = MATCHexact;

        Expression ei = isExpression(oarg);
        Type vt;

        if (!ei && oarg)
        {
            Dsymbol si = isDsymbol(oarg);
            FuncDeclaration f = si ? si.isFuncDeclaration() : null;
            if (!f || !f.fbody || f.needThis())
                goto Lnomatch;

            ei = new VarExp(loc, f);
            ei = ei.semantic(sc);

            /* If a function is really property-like, and then
             * it's CTFEable, ei will be a literal expression.
             */
            uint olderrors = global.startGagging();
            ei = resolveProperties(sc, ei);
            ei = ei.ctfeInterpret();
            if (global.endGagging(olderrors) || ei.op == TOKerror)
                goto Lnomatch;

            /* https://issues.dlang.org/show_bug.cgi?id=14520
             * A property-like function can match to both
             * TemplateAlias and ValueParameter. But for template overloads,
             * it should always prefer alias parameter to be consistent
             * template match result.
             *
             *   template X(alias f) { enum X = 1; }
             *   template X(int val) { enum X = 2; }
             *   int f1() { return 0; }  // CTFEable
             *   int f2();               // body-less function is not CTFEable
             *   enum x1 = X!f1;    // should be 1
             *   enum x2 = X!f2;    // should be 1
             *
             * e.g. The x1 value must be same even if the f1 definition will be moved
             *      into di while stripping body code.
             */
            m = MATCHconvert;
        }

        if (ei && ei.op == TOKvar)
        {
            // Resolve const variables that we had skipped earlier
            ei = ei.ctfeInterpret();
        }

        //printf("\tvalType: %s, ty = %d\n", valType.toChars(), valType.ty);
        vt = valType.semantic(loc, sc);
        //printf("ei: %s, ei.type: %s\n", ei.toChars(), ei.type.toChars());
        //printf("vt = %s\n", vt.toChars());

        if (ei.type)
        {
            MATCH m2 = ei.implicitConvTo(vt);
            //printf("m: %d\n", m);
            if (m2 < m)
                m = m2;
            if (m <= MATCHnomatch)
                goto Lnomatch;
            ei = ei.implicitCastTo(sc, vt);
            ei = ei.ctfeInterpret();
        }

        if (specValue)
        {
            if (!ei || cast(Expression)dmd_aaGetRvalue(edummies, cast(void*)ei.type) == ei)
                goto Lnomatch;

            Expression e = specValue;

            sc = sc.startCTFE();
            e = e.semantic(sc);
            e = resolveProperties(sc, e);
            sc = sc.endCTFE();
            e = e.implicitCastTo(sc, vt);
            e = e.ctfeInterpret();

            ei = ei.syntaxCopy();
            sc = sc.startCTFE();
            ei = ei.semantic(sc);
            sc = sc.endCTFE();
            ei = ei.implicitCastTo(sc, vt);
            ei = ei.ctfeInterpret();
            //printf("\tei: %s, %s\n", ei.toChars(), ei.type.toChars());
            //printf("\te : %s, %s\n", e.toChars(), e.type.toChars());
            if (!ei.equals(e))
                goto Lnomatch;
        }
        else
        {
            if ((*dedtypes)[i])
            {
                // Must match already deduced value
                Expression e = cast(Expression)(*dedtypes)[i];
                if (!ei || !ei.equals(e))
                    goto Lnomatch;
            }
        }
        (*dedtypes)[i] = ei;

        if (psparam)
        {
            Initializer _init = new ExpInitializer(loc, ei);
            Declaration sparam = new VarDeclaration(loc, vt, ident, _init);
            sparam.storage_class = STCmanifest;
            *psparam = sparam;
        }
        return dependent ? MATCHexact : m;

    Lnomatch:
        //printf("\tno match\n");
        if (psparam)
            *psparam = null;
        return MATCHnomatch;
    }

    override void* dummyArg()
    {
        Expression e = specValue;
        if (!e)
        {
            // Create a dummy value
            Expression* pe = cast(Expression*)dmd_aaGet(&edummies, cast(void*)valType);
            if (!*pe)
                *pe = valType.defaultInit();
            e = *pe;
        }
        return cast(void*)e;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

private RootObject aliasParameterSemantic(Loc loc, Scope* sc, RootObject o, TemplateParameters* parameters)
{
    if (o)
    {
        Expression ea = isExpression(o);
        Type ta = isType(o);
        if (ta && (!parameters || !reliesOnTident(ta, parameters)))
        {
            Dsymbol s = ta.toDsymbol(sc);
            if (s)
                o = s;
            else
                o = ta.semantic(loc, sc);
        }
        else if (ea)
        {
            sc = sc.startCTFE();
            ea = ea.semantic(sc);
            sc = sc.endCTFE();
            o = ea.ctfeInterpret();
        }
    }
    return o;
}

/***********************************************************
 * Syntax:
 *  specType ident : specAlias = defaultAlias
 */
extern (C++) final class TemplateAliasParameter : TemplateParameter
{
    Type specType;
    RootObject specAlias;
    RootObject defaultAlias;

    extern (C++) static __gshared Dsymbol sdummy = null;

    extern (D) this(Loc loc, Identifier ident, Type specType, RootObject specAlias, RootObject defaultAlias)
    {
        super(loc, ident);
        this.ident = ident;
        this.specType = specType;
        this.specAlias = specAlias;
        this.defaultAlias = defaultAlias;
    }

    override TemplateAliasParameter isTemplateAliasParameter()
    {
        return this;
    }

    override TemplateParameter syntaxCopy()
    {
        return new TemplateAliasParameter(loc, ident, specType ? specType.syntaxCopy() : null, objectSyntaxCopy(specAlias), objectSyntaxCopy(defaultAlias));
    }

    override bool declareParameter(Scope* sc)
    {
        auto ti = new TypeIdentifier(loc, ident);
        Declaration ad = new AliasDeclaration(loc, ident, ti);
        return sc.insert(ad) !is null;
    }

    override bool semantic(Scope* sc, TemplateParameters* parameters)
    {
        if (specType && !reliesOnTident(specType, parameters))
        {
            specType = specType.semantic(loc, sc);
        }
        specAlias = aliasParameterSemantic(loc, sc, specAlias, parameters);
        version (none)
        {
            // Don't do semantic() until instantiation
            if (defaultAlias)
                defaultAlias = defaultAlias.semantic(loc, sc);
        }
        return !(specType && isError(specType)) && !(specAlias && isError(specAlias));
    }

    override void print(RootObject oarg, RootObject oded)
    {
        printf(" %s\n", ident.toChars());
        Dsymbol sa = isDsymbol(oded);
        assert(sa);
        printf("\tParameter alias: %s\n", sa.toChars());
    }

    override RootObject specialization()
    {
        return specAlias;
    }

    override RootObject defaultArg(Loc instLoc, Scope* sc)
    {
        RootObject da = defaultAlias;
        Type ta = isType(defaultAlias);
        if (ta)
        {
            if (ta.ty == Tinstance)
            {
                // If the default arg is a template, instantiate for each type
                da = ta.syntaxCopy();
            }
        }

        RootObject o = aliasParameterSemantic(loc, sc, da, null); // use the parameter loc
        return o;
    }

    override bool hasDefaultArg()
    {
        return defaultAlias !is null;
    }

    override MATCH matchArg(Scope* sc, RootObject oarg, size_t i, TemplateParameters* parameters, Objects* dedtypes, Declaration* psparam)
    {
        //printf("TemplateAliasParameter.matchArg('%s')\n", ident.toChars());
        MATCH m = MATCHexact;
        Type ta = isType(oarg);
        RootObject sa = ta && !ta.deco ? null : getDsymbol(oarg);
        Expression ea = isExpression(oarg);
        if (ea && (ea.op == TOKthis || ea.op == TOKsuper))
            sa = (cast(ThisExp)ea).var;
        else if (ea && ea.op == TOKscope)
            sa = (cast(ScopeExp)ea).sds;
        if (sa)
        {
            if ((cast(Dsymbol)sa).isAggregateDeclaration())
                m = MATCHconvert;

            /* specType means the alias must be a declaration with a type
             * that matches specType.
             */
            if (specType)
            {
                Declaration d = (cast(Dsymbol)sa).isDeclaration();
                if (!d)
                    goto Lnomatch;
                if (!d.type.equals(specType))
                    goto Lnomatch;
            }
        }
        else
        {
            sa = oarg;
            if (ea)
            {
                if (specType)
                {
                    if (!ea.type.equals(specType))
                        goto Lnomatch;
                }
            }
            else if (ta && ta.ty == Tinstance && !specAlias)
            {
                /* Specialized parameter should be preferred
                 * match to the template type parameter.
                 *  template X(alias a) {}                      // a == this
                 *  template X(alias a : B!A, alias B, A...) {} // B!A => ta
                 */
            }
            else if (sa && sa == TemplateTypeParameter.tdummy)
            {
                /* https://issues.dlang.org/show_bug.cgi?id=2025
                 * Aggregate Types should preferentially
                 * match to the template type parameter.
                 *  template X(alias a) {}  // a == this
                 *  template X(T) {}        // T => sa
                 */
            }
            else
                goto Lnomatch;
        }

        if (specAlias)
        {
            if (sa == sdummy)
                goto Lnomatch;
            Dsymbol sx = isDsymbol(sa);
            if (sa != specAlias && sx)
            {
                Type talias = isType(specAlias);
                if (!talias)
                    goto Lnomatch;

                TemplateInstance ti = sx.isTemplateInstance();
                if (!ti && sx.parent)
                {
                    ti = sx.parent.isTemplateInstance();
                    if (ti && ti.name != sx.ident)
                        goto Lnomatch;
                }
                if (!ti)
                    goto Lnomatch;

                Type t = new TypeInstance(Loc(), ti);
                MATCH m2 = deduceType(t, sc, talias, parameters, dedtypes);
                if (m2 <= MATCHnomatch)
                    goto Lnomatch;
            }
        }
        else if ((*dedtypes)[i])
        {
            // Must match already deduced symbol
            RootObject si = (*dedtypes)[i];
            if (!sa || si != sa)
                goto Lnomatch;
        }
        (*dedtypes)[i] = sa;

        if (psparam)
        {
            if (Dsymbol s = isDsymbol(sa))
            {
                *psparam = new AliasDeclaration(loc, ident, s);
            }
            else if (Type t = isType(sa))
            {
                *psparam = new AliasDeclaration(loc, ident, t);
            }
            else
            {
                assert(ea);

                // Declare manifest constant
                Initializer _init = new ExpInitializer(loc, ea);
                auto v = new VarDeclaration(loc, null, ident, _init);
                v.storage_class = STCmanifest;
                v.semantic(sc);
                *psparam = v;
            }
        }
        return dependent ? MATCHexact : m;

    Lnomatch:
        if (psparam)
            *psparam = null;
        //printf("\tm = %d\n", MATCHnomatch);
        return MATCHnomatch;
    }

    override void* dummyArg()
    {
        RootObject s = specAlias;
        if (!s)
        {
            if (!sdummy)
                sdummy = new Dsymbol();
            s = sdummy;
        }
        return cast(void*)s;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/***********************************************************
 * Syntax:
 *  ident ...
 */
extern (C++) final class TemplateTupleParameter : TemplateParameter
{
    extern (D) this(Loc loc, Identifier ident)
    {
        super(loc, ident);
        this.ident = ident;
    }

    override TemplateTupleParameter isTemplateTupleParameter()
    {
        return this;
    }

    override TemplateParameter syntaxCopy()
    {
        return new TemplateTupleParameter(loc, ident);
    }

    override bool declareParameter(Scope* sc)
    {
        auto ti = new TypeIdentifier(loc, ident);
        Declaration ad = new AliasDeclaration(loc, ident, ti);
        return sc.insert(ad) !is null;
    }

    override bool semantic(Scope* sc, TemplateParameters* parameters)
    {
        return true;
    }

    override void print(RootObject oarg, RootObject oded)
    {
        printf(" %s... [", ident.toChars());
        Tuple v = isTuple(oded);
        assert(v);

        //printf("|%d| ", v.objects.dim);
        for (size_t i = 0; i < v.objects.dim; i++)
        {
            if (i)
                printf(", ");

            RootObject o = v.objects[i];
            Dsymbol sa = isDsymbol(o);
            if (sa)
                printf("alias: %s", sa.toChars());
            Type ta = isType(o);
            if (ta)
                printf("type: %s", ta.toChars());
            Expression ea = isExpression(o);
            if (ea)
                printf("exp: %s", ea.toChars());

            assert(!isTuple(o)); // no nested Tuple arguments
        }
        printf("]\n");
    }

    override RootObject specialization()
    {
        return null;
    }

    override RootObject defaultArg(Loc instLoc, Scope* sc)
    {
        return null;
    }

    override bool hasDefaultArg()
    {
        return false;
    }

    override MATCH matchArg(Loc instLoc, Scope* sc, Objects* tiargs, size_t i, TemplateParameters* parameters, Objects* dedtypes, Declaration* psparam)
    {
        /* The rest of the actual arguments (tiargs[]) form the match
         * for the variadic parameter.
         */
        assert(i + 1 == dedtypes.dim); // must be the last one
        Tuple ovar;

        if (Tuple u = isTuple((*dedtypes)[i]))
        {
            // It has already been deduced
            ovar = u;
        }
        else if (i + 1 == tiargs.dim && isTuple((*tiargs)[i]))
            ovar = isTuple((*tiargs)[i]);
        else
        {
            ovar = new Tuple();
            //printf("ovar = %p\n", ovar);
            if (i < tiargs.dim)
            {
                //printf("i = %d, tiargs.dim = %d\n", i, tiargs.dim);
                ovar.objects.setDim(tiargs.dim - i);
                for (size_t j = 0; j < ovar.objects.dim; j++)
                    ovar.objects[j] = (*tiargs)[i + j];
            }
        }
        return matchArg(sc, ovar, i, parameters, dedtypes, psparam);
    }

    override MATCH matchArg(Scope* sc, RootObject oarg, size_t i, TemplateParameters* parameters, Objects* dedtypes, Declaration* psparam)
    {
        //printf("TemplateTupleParameter.matchArg('%s')\n", ident.toChars());
        Tuple ovar = isTuple(oarg);
        if (!ovar)
            return MATCHnomatch;
        if ((*dedtypes)[i])
        {
            Tuple tup = isTuple((*dedtypes)[i]);
            if (!tup)
                return MATCHnomatch;
            if (!match(tup, ovar))
                return MATCHnomatch;
        }
        (*dedtypes)[i] = ovar;

        if (psparam)
            *psparam = new TupleDeclaration(loc, ident, &ovar.objects);
        return dependent ? MATCHexact : MATCHconvert;
    }

    override void* dummyArg()
    {
        return null;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/***********************************************************
 * Given:
 *  foo!(args) =>
 *      name = foo
 *      tiargs = args
 */
extern (C++) class TemplateInstance : ScopeDsymbol
{
    Identifier name;

    // Array of Types/Expressions of template
    // instance arguments [int*, char, 10*10]
    Objects* tiargs;

    // Array of Types/Expressions corresponding
    // to TemplateDeclaration.parameters
    // [int, char, 100]
    Objects tdtypes;

    Dsymbol tempdecl;           // referenced by foo.bar.abc
    Dsymbol enclosing;          // if referencing local symbols, this is the context
    Dsymbol aliasdecl;          // !=null if instance is an alias for its sole member
    TemplateInstance inst;      // refer to existing instance
    ScopeDsymbol argsym;        // argument symbol table
    int inuse;                  // for recursive expansion detection
    int nest;                   // for recursive pretty printing detection
    bool semantictiargsdone;    // has semanticTiargs() been done?
    bool havetempdecl;          // if used second constructor
    bool gagged;                // if the instantiation is done with error gagging
    hash_t hash;                // cached result of toHash()
    Expressions* fargs;         // for function template, these are the function arguments

    TemplateInstances* deferred;

    Module memberOf;            // if !null, then this TemplateInstance appears in memberOf.members[]

    // Used to determine the instance needs code generation.
    // Note that these are inaccurate until semantic analysis phase completed.
    TemplateInstance tinst;     // enclosing template instance
    TemplateInstance tnext;     // non-first instantiated instances
    Module minst;               // the top module that instantiated this instance

    final extern (D) this(Loc loc, Identifier ident, Objects* tiargs)
    {
        super(null);
        static if (LOG)
        {
            printf("TemplateInstance(this = %p, ident = '%s')\n", this, ident ? ident.toChars() : "null");
        }
        this.loc = loc;
        this.name = ident;
        this.tiargs = tiargs;
    }

    /*****************
     * This constructor is only called when we figured out which function
     * template to instantiate.
     */
    final extern (D) this(Loc loc, TemplateDeclaration td, Objects* tiargs)
    {
        super(null);
        static if (LOG)
        {
            printf("TemplateInstance(this = %p, tempdecl = '%s')\n", this, td.toChars());
        }
        this.loc = loc;
        this.name = td.ident;
        this.tiargs = tiargs;
        this.tempdecl = td;
        this.semantictiargsdone = true;
        this.havetempdecl = true;
        assert(tempdecl._scope);
    }

    static Objects* arraySyntaxCopy(Objects* objs)
    {
        Objects* a = null;
        if (objs)
        {
            a = new Objects();
            a.setDim(objs.dim);
            for (size_t i = 0; i < objs.dim; i++)
                (*a)[i] = objectSyntaxCopy((*objs)[i]);
        }
        return a;
    }

    override Dsymbol syntaxCopy(Dsymbol s)
    {
        TemplateInstance ti = s ? cast(TemplateInstance)s : new TemplateInstance(loc, name, null);
        ti.tiargs = arraySyntaxCopy(tiargs);
        TemplateDeclaration td;
        if (inst && tempdecl && (td = tempdecl.isTemplateDeclaration()) !is null)
            td.ScopeDsymbol.syntaxCopy(ti);
        else
            ScopeDsymbol.syntaxCopy(ti);
        return ti;
    }

    void semantic(Scope* sc, Expressions* fargs)
    {
        //printf("[%s] TemplateInstance.semantic('%s', this=%p, gag = %d, sc = %p)\n", loc.toChars(), toChars(), this, global.gag, sc);
        version (none)
        {
            for (Dsymbol s = this; s; s = s.parent)
            {
                printf("\t%s\n", s.toChars());
            }
            printf("Scope\n");
            for (Scope* scx = sc; scx; scx = scx.enclosing)
            {
                printf("\t%s parent %s\n", scx._module ? scx._module.toChars() : "null", scx.parent ? scx.parent.toChars() : "null");
            }
        }

        static if (LOG)
        {
            printf("\n+TemplateInstance.semantic('%s', this=%p)\n", toChars(), this);
        }
        if (inst) // if semantic() was already run
        {
            static if (LOG)
            {
                printf("-TemplateInstance.semantic('%s', this=%p) already run\n", inst.toChars(), inst);
            }
            return;
        }
        if (semanticRun != PASSinit)
        {
            static if (LOG)
            {
                printf("Recursive template expansion\n");
            }
            auto ungag = Ungag(global.gag);
            if (!gagged)
                global.gag = 0;
            error(loc, "recursive template expansion");
            if (gagged)
                semanticRun = PASSinit;
            else
                inst = this;
            errors = true;
            return;
        }

        // Get the enclosing template instance from the scope tinst
        tinst = sc.tinst;

        // Get the instantiating module from the scope minst
        minst = sc.minst;
        // https://issues.dlang.org/show_bug.cgi?id=10920
        // If the enclosing function is non-root symbol,
        // this instance should be speculative.
        if (!tinst && sc.func && sc.func.inNonRoot())
        {
            minst = null;
        }

        gagged = (global.gag > 0);

        semanticRun = PASSsemantic;

        static if (LOG)
        {
            printf("\tdo semantic\n");
        }
        /* Find template declaration first,
         * then run semantic on each argument (place results in tiargs[]),
         * last find most specialized template from overload list/set.
         */
        if (!findTempDecl(sc, null) || !semanticTiargs(sc) || !findBestMatch(sc, fargs))
        {
        Lerror:
            if (gagged)
            {
                // https://issues.dlang.org/show_bug.cgi?id=13220
                // Roll back status for later semantic re-running
                semanticRun = PASSinit;
            }
            else
                inst = this;
            errors = true;
            return;
        }
        TemplateDeclaration tempdecl = this.tempdecl.isTemplateDeclaration();
        assert(tempdecl);

        // If tempdecl is a mixin, disallow it
        if (tempdecl.ismixin)
        {
            error("mixin templates are not regular templates");
            goto Lerror;
        }

        hasNestedArgs(tiargs, tempdecl.isstatic);
        if (errors)
            goto Lerror;

        /* See if there is an existing TemplateInstantiation that already
         * implements the typeargs. If so, just refer to that one instead.
         */
        inst = tempdecl.findExistingInstance(this, fargs);
        TemplateInstance errinst = null;
        if (!inst)
        {
            // So, we need to implement 'this' instance.
        }
        else if (inst.gagged && !gagged && inst.errors)
        {
            // If the first instantiation had failed, re-run semantic,
            // so that error messages are shown.
            errinst = inst;
        }
        else
        {
            // It's a match
            parent = inst.parent;
            errors = inst.errors;

            // If both this and the previous instantiation were gagged,
            // use the number of errors that happened last time.
            global.errors += errors;
            global.gaggedErrors += errors;

            // If the first instantiation was gagged, but this is not:
            if (inst.gagged)
            {
                // It had succeeded, mark it is a non-gagged instantiation,
                // and reuse it.
                inst.gagged = gagged;
            }

            this.tnext = inst.tnext;
            inst.tnext = this;

            /* A module can have explicit template instance and its alias
             * in module scope (e,g, `alias Base64 = Base64Impl!('+', '/');`).
             * If the first instantiation 'inst' had happened in non-root module,
             * compiler can assume that its instantiated code would be included
             * in the separately compiled obj/lib file (e.g. phobos.lib).
             *
             * However, if 'this' second instantiation happened in root module,
             * compiler might need to invoke its codegen
             * (https://issues.dlang.org/show_bug.cgi?id=2500 & https://issues.dlang.org/show_bug.cgi?id=2644).
             * But whole import graph is not determined until all semantic pass finished,
             * so 'inst' should conservatively finish the semantic3 pass for the codegen.
             */
            if (minst && minst.isRoot() && !(inst.minst && inst.minst.isRoot()))
            {
                /* Swap the position of 'inst' and 'this' in the instantiation graph.
                 * Then, the primary instance `inst` will be changed to a root instance.
                 *
                 * Before:
                 *  non-root -> A!() -> B!()[inst] -> C!()
                 *                      |
                 *  root     -> D!() -> B!()[this]
                 *
                 * After:
                 *  non-root -> A!() -> B!()[this]
                 *                      |
                 *  root     -> D!() -> B!()[inst] -> C!()
                 */
                Module mi = minst;
                TemplateInstance ti = tinst;
                minst = inst.minst;
                tinst = inst.tinst;
                inst.minst = mi;
                inst.tinst = ti;

                if (minst) // if inst was not speculative
                {
                    /* Add 'inst' once again to the root module members[], then the
                     * instance members will get codegen chances.
                     */
                    inst.appendToModuleMember();
                }
            }
            static if (LOG)
            {
                printf("\tit's a match with instance %p, %d\n", inst, inst.semanticRun);
            }
            return;
        }
        static if (LOG)
        {
            printf("\timplement template instance %s '%s'\n", tempdecl.parent.toChars(), toChars());
            printf("\ttempdecl %s\n", tempdecl.toChars());
        }
        uint errorsave = global.errors;

        inst = this;
        parent = enclosing ? enclosing : tempdecl.parent;
        //printf("parent = '%s'\n", parent.kind());

        TemplateInstance tempdecl_instance_idx = tempdecl.addInstance(this);

        //getIdent();

        // Store the place we added it to in target_symbol_list(_idx) so we can
        // remove it later if we encounter an error.
        Dsymbols* target_symbol_list = appendToModuleMember();
        size_t target_symbol_list_idx = target_symbol_list ? target_symbol_list.dim - 1 : 0;

        // Copy the syntax trees from the TemplateDeclaration
        members = Dsymbol.arraySyntaxCopy(tempdecl.members);

        // resolve TemplateThisParameter
        for (size_t i = 0; i < tempdecl.parameters.dim; i++)
        {
            if ((*tempdecl.parameters)[i].isTemplateThisParameter() is null)
                continue;
            Type t = isType((*tiargs)[i]);
            assert(t);
            if (StorageClass stc = ModToStc(t.mod))
            {
                //printf("t = %s, stc = x%llx\n", t.toChars(), stc);
                auto s = new Dsymbols();
                s.push(new StorageClassDeclaration(stc, members));
                members = s;
            }
            break;
        }

        // Create our own scope for the template parameters
        Scope* _scope = tempdecl._scope;
        if (tempdecl.semanticRun == PASSinit)
        {
            error("template instantiation %s forward references template declaration %s", toChars(), tempdecl.toChars());
            return;
        }

        static if (LOG)
        {
            printf("\tcreate scope for template parameters '%s'\n", toChars());
        }
        argsym = new ScopeDsymbol();
        argsym.parent = _scope.parent;
        _scope = _scope.push(argsym);
        _scope.tinst = this;
        _scope.minst = minst;
        //scope.stc = 0;

        // Declare each template parameter as an alias for the argument type
        Scope* paramscope = _scope.push();
        paramscope.stc = 0;
        paramscope.protection = Prot(PROTpublic); // https://issues.dlang.org/show_bug.cgi?id=14169
                                                  // template parameters should be public
        declareParameters(paramscope);
        paramscope.pop();

        // Add members of template instance to template instance symbol table
        //parent = scope.scopesym;
        symtab = new DsymbolTable();
        for (size_t i = 0; i < members.dim; i++)
        {
            Dsymbol s = (*members)[i];
            static if (LOG)
            {
                printf("\t[%d] adding member '%s' %p kind %s to '%s'\n", i, s.toChars(), s, s.kind(), this.toChars());
            }
            s.addMember(_scope, this);
        }
        static if (LOG)
        {
            printf("adding members done\n");
        }

        /* See if there is only one member of template instance, and that
         * member has the same name as the template instance.
         * If so, this template instance becomes an alias for that member.
         */
        //printf("members.dim = %d\n", members.dim);
        if (members.dim)
        {
            Dsymbol s;
            if (Dsymbol.oneMembers(members, &s, tempdecl.ident) && s)
            {
                //printf("tempdecl.ident = %s, s = '%s'\n", tempdecl.ident.toChars(), s.kind(), s.toPrettyChars());
                //printf("setting aliasdecl\n");
                aliasdecl = s;
            }
        }

        /* If function template declaration
         */
        if (fargs && aliasdecl)
        {
            FuncDeclaration fd = aliasdecl.isFuncDeclaration();
            if (fd)
            {
                /* Transmit fargs to type so that TypeFunction.semantic() can
                 * resolve any "auto ref" storage classes.
                 */
                TypeFunction tf = cast(TypeFunction)fd.type;
                if (tf && tf.ty == Tfunction)
                    tf.fargs = fargs;
            }
        }

        // Do semantic() analysis on template instance members
        static if (LOG)
        {
            printf("\tdo semantic() on template instance members '%s'\n", toChars());
        }
        Scope* sc2;
        sc2 = _scope.push(this);
        //printf("enclosing = %d, sc.parent = %s\n", enclosing, sc.parent.toChars());
        sc2.parent = this;
        sc2.tinst = this;
        sc2.minst = minst;

        tryExpandMembers(sc2);

        semanticRun = PASSsemanticdone;

        /* ConditionalDeclaration may introduce eponymous declaration,
         * so we should find it once again after semantic.
         */
        if (members.dim)
        {
            Dsymbol s;
            if (Dsymbol.oneMembers(members, &s, tempdecl.ident) && s)
            {
                if (!aliasdecl || aliasdecl != s)
                {
                    //printf("tempdecl.ident = %s, s = '%s'\n", tempdecl.ident.toChars(), s.kind(), s.toPrettyChars());
                    //printf("setting aliasdecl 2\n");
                    aliasdecl = s;
                }
            }
        }

        if (global.errors != errorsave)
            goto Laftersemantic;

        /* If any of the instantiation members didn't get semantic() run
         * on them due to forward references, we cannot run semantic2()
         * or semantic3() yet.
         */
        {
            bool found_deferred_ad = false;
            for (size_t i = 0; i < Module.deferred.dim; i++)
            {
                Dsymbol sd = Module.deferred[i];
                AggregateDeclaration ad = sd.isAggregateDeclaration();
                if (ad && ad.parent && ad.parent.isTemplateInstance())
                {
                    //printf("deferred template aggregate: %s %s\n",
                    //        sd.parent.toChars(), sd.toChars());
                    found_deferred_ad = true;
                    if (ad.parent == this)
                    {
                        ad.deferred = this;
                        break;
                    }
                }
            }
            if (found_deferred_ad || Module.deferred.dim)
                goto Laftersemantic;
        }

        /* The problem is when to parse the initializer for a variable.
         * Perhaps VarDeclaration.semantic() should do it like it does
         * for initializers inside a function.
         */
        //if (sc.parent.isFuncDeclaration())
        {
            /* https://issues.dlang.org/show_bug.cgi?id=782
             * this has problems if the classes this depends on
             * are forward referenced. Find a way to defer semantic()
             * on this template.
             */
            semantic2(sc2);
        }
        if (global.errors != errorsave)
            goto Laftersemantic;

        if ((sc.func || (sc.flags & SCOPEfullinst)) && !tinst)
        {
            /* If a template is instantiated inside function, the whole instantiation
             * should be done at that position. But, immediate running semantic3 of
             * dependent templates may cause unresolved forward reference.
             * https://issues.dlang.org/show_bug.cgi?id=9050
             * To avoid the issue, don't run semantic3 until semantic and semantic2 done.
             */
            TemplateInstances deferred;
            this.deferred = &deferred;

            //printf("Run semantic3 on %s\n", toChars());
            trySemantic3(sc2);

            for (size_t i = 0; i < deferred.dim; i++)
            {
                //printf("+ run deferred semantic3 on %s\n", deferred[i].toChars());
                deferred[i].semantic3(null);
            }

            this.deferred = null;
        }
        else if (tinst)
        {
            bool doSemantic3 = false;
            if (sc.func && aliasdecl && aliasdecl.toAlias().isFuncDeclaration())
            {
                /* Template function instantiation should run semantic3 immediately
                 * for attribute inference.
                 */
                doSemantic3 = true;
            }
            else if (sc.func)
            {
                /* A lambda function in template arguments might capture the
                 * instantiated scope context. For the correct context inference,
                 * all instantiated functions should run the semantic3 immediately.
                 * See also compilable/test14973.d
                 */
                foreach (oarg; tdtypes)
                {
                    auto s = getDsymbol(oarg);
                    if (!s)
                        continue;

                    if (auto td = s.isTemplateDeclaration())
                    {
                        if (!td.literal)
                            continue;
                        assert(td.members && td.members.dim == 1);
                        s = (*td.members)[0];
                    }
                    if (auto fld = s.isFuncLiteralDeclaration())
                    {
                        if (fld.tok == TOKreserved)
                        {
                            doSemantic3 = true;
                            break;
                        }
                    }
                }
                //printf("[%s] %s doSemantic3 = %d\n", loc.toChars(), toChars(), doSemantic3);
            }
            if (doSemantic3)
                trySemantic3(sc2);

            TemplateInstance ti = tinst;
            int nest = 0;
            while (ti && !ti.deferred && ti.tinst)
            {
                ti = ti.tinst;
                if (++nest > 500)
                {
                    global.gag = 0; // ensure error message gets printed
                    error("recursive expansion");
                    fatal();
                }
            }
            if (ti && ti.deferred)
            {
                //printf("deferred semantic3 of %p %s, ti = %s, ti.deferred = %p\n", this, toChars(), ti.toChars());
                for (size_t i = 0;; i++)
                {
                    if (i == ti.deferred.dim)
                    {
                        ti.deferred.push(this);
                        break;
                    }
                    if ((*ti.deferred)[i] == this)
                        break;
                }
            }
        }

        if (aliasdecl)
        {
            /* https://issues.dlang.org/show_bug.cgi?id=13816
             * AliasDeclaration tries to resolve forward reference
             * twice (See inuse check in AliasDeclaration.toAlias()). It's
             * necessary to resolve mutual references of instantiated symbols, but
             * it will left a true recursive alias in tuple declaration - an
             * AliasDeclaration A refers TupleDeclaration B, and B contains A
             * in its elements.  To correctly make it an error, we strictly need to
             * resolve the alias of eponymous member.
             */
            aliasdecl = aliasdecl.toAlias2();
        }

    Laftersemantic:
        sc2.pop();
        _scope.pop();

        // Give additional context info if error occurred during instantiation
        if (global.errors != errorsave)
        {
            if (!errors)
            {
                if (!tempdecl.literal)
                    error(loc, "error instantiating");
                if (tinst)
                    tinst.printInstantiationTrace();
            }
            errors = true;
            if (gagged)
            {
                // Errors are gagged, so remove the template instance from the
                // instance/symbol lists we added it to and reset our state to
                // finish clean and so we can try to instantiate it again later
                // (see https://issues.dlang.org/show_bug.cgi?id=4302 and https://issues.dlang.org/show_bug.cgi?id=6602).
                tempdecl.removeInstance(tempdecl_instance_idx);
                if (target_symbol_list)
                {
                    // Because we added 'this' in the last position above, we
                    // should be able to remove it without messing other indices up.
                    assert((*target_symbol_list)[target_symbol_list_idx] == this);
                    target_symbol_list.remove(target_symbol_list_idx);
                    memberOf = null;                    // no longer a member
                }
                semanticRun = PASSinit;
                inst = null;
                symtab = null;
            }
        }
        else if (errinst)
        {
            /* https://issues.dlang.org/show_bug.cgi?id=14541
             * If the previous gagged instance had failed by
             * circular references, currrent "error reproduction instantiation"
             * might succeed, because of the difference of instantiated context.
             * On such case, the cached error instance needs to be overridden by the
             * succeeded instance.
             */
            //printf("replaceInstance()\n");
            assert(errinst.errors);
            auto ti1 = TemplateInstanceBox(errinst);
            tempdecl.instances.remove(ti1);

            auto ti2 = TemplateInstanceBox(this);
            tempdecl.instances[ti2] = this;
        }

        static if (LOG)
        {
            printf("-TemplateInstance.semantic('%s', this=%p)\n", toChars(), this);
        }
    }

    override void semantic(Scope* sc)
    {
        semantic(sc, null);
    }

    override void semantic2(Scope* sc)
    {
        if (semanticRun >= PASSsemantic2)
            return;
        semanticRun = PASSsemantic2;
        static if (LOG)
        {
            printf("+TemplateInstance.semantic2('%s')\n", toChars());
        }
        if (!errors && members)
        {
            TemplateDeclaration tempdecl = this.tempdecl.isTemplateDeclaration();
            assert(tempdecl);

            sc = tempdecl._scope;
            assert(sc);
            sc = sc.push(argsym);
            sc = sc.push(this);
            sc.tinst = this;
            sc.minst = minst;

            int needGagging = (gagged && !global.gag);
            uint olderrors = global.errors;
            int oldGaggedErrors = -1; // dead-store to prevent spurious warning
            if (needGagging)
                oldGaggedErrors = global.startGagging();

            for (size_t i = 0; i < members.dim; i++)
            {
                Dsymbol s = (*members)[i];
                static if (LOG)
                {
                    printf("\tmember '%s', kind = '%s'\n", s.toChars(), s.kind());
                }
                s.semantic2(sc);
                if (gagged && global.errors != olderrors)
                    break;
            }

            if (global.errors != olderrors)
            {
                if (!errors)
                {
                    if (!tempdecl.literal)
                        error(loc, "error instantiating");
                    if (tinst)
                        tinst.printInstantiationTrace();
                }
                errors = true;
            }
            if (needGagging)
                global.endGagging(oldGaggedErrors);

            sc = sc.pop();
            sc.pop();
        }
        static if (LOG)
        {
            printf("-TemplateInstance.semantic2('%s')\n", toChars());
        }
    }

    override void semantic3(Scope* sc)
    {
        static if (LOG)
        {
            printf("TemplateInstance.semantic3('%s'), semanticRun = %d\n", toChars(), semanticRun);
        }
        //if (toChars()[0] == 'D') *(char*)0=0;
        if (semanticRun >= PASSsemantic3)
            return;
        semanticRun = PASSsemantic3;
        if (!errors && members)
        {
            TemplateDeclaration tempdecl = this.tempdecl.isTemplateDeclaration();
            assert(tempdecl);

            sc = tempdecl._scope;
            sc = sc.push(argsym);
            sc = sc.push(this);
            sc.tinst = this;
            sc.minst = minst;

            int needGagging = (gagged && !global.gag);
            uint olderrors = global.errors;
            int oldGaggedErrors = -1; // dead-store to prevent spurious warning
            /* If this is a gagged instantiation, gag errors.
             * Future optimisation: If the results are actually needed, errors
             * would already be gagged, so we don't really need to run semantic
             * on the members.
             */
            if (needGagging)
                oldGaggedErrors = global.startGagging();

            for (size_t i = 0; i < members.dim; i++)
            {
                Dsymbol s = (*members)[i];
                s.semantic3(sc);
                if (gagged && global.errors != olderrors)
                    break;
            }

            if (global.errors != olderrors)
            {
                if (!errors)
                {
                    if (!tempdecl.literal)
                        error(loc, "error instantiating");
                    if (tinst)
                        tinst.printInstantiationTrace();
                }
                errors = true;
            }
            if (needGagging)
                global.endGagging(oldGaggedErrors);

            sc = sc.pop();
            sc.pop();
        }
    }

    // resolve real symbol
    override final Dsymbol toAlias()
    {
        static if (LOG)
        {
            printf("TemplateInstance.toAlias()\n");
        }
        if (!inst)
        {
            // Maybe we can resolve it
            if (_scope)
            {
                semantic(_scope);
            }
            if (!inst)
            {
                error("cannot resolve forward reference");
                errors = true;
                return this;
            }
        }

        if (inst != this)
            return inst.toAlias();

        if (aliasdecl)
        {
            return aliasdecl.toAlias();
        }

        return inst;
    }

    override const(char)* kind() const
    {
        return "template instance";
    }

    override bool oneMember(Dsymbol* ps, Identifier ident)
    {
        *ps = null;
        return true;
    }

    override const(char)* toChars()
    {
        OutBuffer buf;
        toCBufferInstance(this, &buf);
        return buf.extractString();
    }

    override final const(char)* toPrettyCharsHelper()
    {
        OutBuffer buf;
        toCBufferInstance(this, &buf, true);
        return buf.extractString();
    }

    /**************************************
     * Given an error instantiating the TemplateInstance,
     * give the nested TemplateInstance instantiations that got
     * us here. Those are a list threaded into the nested scopes.
     */
    final void printInstantiationTrace()
    {
        if (global.gag)
            return;

        const(uint) max_shown = 6;
        const(char)* format = "instantiated from here: %s";

        // determine instantiation depth and number of recursive instantiations
        int n_instantiations = 1;
        int n_totalrecursions = 0;
        for (TemplateInstance cur = this; cur; cur = cur.tinst)
        {
            ++n_instantiations;
            // If two instantiations use the same declaration, they are recursive.
            // (this works even if they are instantiated from different places in the
            // same template).
            // In principle, we could also check for multiple-template recursion, but it's
            // probably not worthwhile.
            if (cur.tinst && cur.tempdecl && cur.tinst.tempdecl && cur.tempdecl.loc.equals(cur.tinst.tempdecl.loc))
                ++n_totalrecursions;
        }

        // show full trace only if it's short or verbose is on
        if (n_instantiations <= max_shown || global.params.verbose)
        {
            for (TemplateInstance cur = this; cur; cur = cur.tinst)
            {
                cur.errors = true;
                errorSupplemental(cur.loc, format, cur.toChars());
            }
        }
        else if (n_instantiations - n_totalrecursions <= max_shown)
        {
            // By collapsing recursive instantiations into a single line,
            // we can stay under the limit.
            int recursionDepth = 0;
            for (TemplateInstance cur = this; cur; cur = cur.tinst)
            {
                cur.errors = true;
                if (cur.tinst && cur.tempdecl && cur.tinst.tempdecl && cur.tempdecl.loc.equals(cur.tinst.tempdecl.loc))
                {
                    ++recursionDepth;
                }
                else
                {
                    if (recursionDepth)
                        errorSupplemental(cur.loc, "%d recursive instantiations from here: %s", recursionDepth + 2, cur.toChars());
                    else
                        errorSupplemental(cur.loc, format, cur.toChars());
                    recursionDepth = 0;
                }
            }
        }
        else
        {
            // Even after collapsing the recursions, the depth is too deep.
            // Just display the first few and last few instantiations.
            uint i = 0;
            for (TemplateInstance cur = this; cur; cur = cur.tinst)
            {
                cur.errors = true;

                if (i == max_shown / 2)
                    errorSupplemental(cur.loc, "... (%d instantiations, -v to show) ...", n_instantiations - max_shown);

                if (i < max_shown / 2 || i >= n_instantiations - max_shown + max_shown / 2)
                    errorSupplemental(cur.loc, format, cur.toChars());
                ++i;
            }
        }
    }

    /*************************************
     * Lazily generate identifier for template instance.
     * This is because 75% of the ident's are never needed.
     */
    override final Identifier getIdent()
    {
        if (!ident && inst && !errors)
            ident = genIdent(tiargs); // need an identifier for name mangling purposes.
        return ident;
    }

    /*************************************
     * Compare proposed template instantiation with existing template instantiation.
     * Note that this is not commutative because of the auto ref check.
     * Params:
     *  this = proposed template instantiation
     *  o = existing template instantiation
     * Returns:
     *  0 for match, 1 for no match
     */
    override final int compare(RootObject o)
    {
        TemplateInstance ti = cast(TemplateInstance)o;

        //printf("this = %p, ti = %p\n", this, ti);
        assert(tdtypes.dim == ti.tdtypes.dim);

        // Nesting must match
        if (enclosing != ti.enclosing)
        {
            //printf("test2 enclosing %s ti.enclosing %s\n", enclosing ? enclosing.toChars() : "", ti.enclosing ? ti.enclosing.toChars() : "");
            goto Lnotequals;
        }
        //printf("parent = %s, ti.parent = %s\n", parent.toPrettyChars(), ti.parent.toPrettyChars());

        if (!arrayObjectMatch(&tdtypes, &ti.tdtypes))
            goto Lnotequals;

        /* Template functions may have different instantiations based on
         * "auto ref" parameters.
         */
        if (auto fd = ti.toAlias().isFuncDeclaration())
        {
            if (!fd.errors)
            {
                auto fparameters = fd.getParameters(null);
                size_t nfparams = Parameter.dim(fparameters);   // Num function parameters
                for (size_t j = 0; j < nfparams; j++)
                {
                    Parameter fparam = Parameter.getNth(fparameters, j);
                    if (fparam.storageClass & STCautoref)       // if "auto ref"
                    {
                        if (!fargs)
                            goto Lnotequals;
                        if (fargs.dim <= j)
                            break;
                        Expression farg = (*fargs)[j];
                        if (farg.isLvalue())
                        {
                            if (!(fparam.storageClass & STCref))
                                goto Lnotequals; // auto ref's don't match
                        }
                        else
                        {
                            if (fparam.storageClass & STCref)
                                goto Lnotequals; // auto ref's don't match
                        }
                    }
                }
            }
        }
        return 0;

    Lnotequals:
        return 1;
    }

    final hash_t toHash()
    {
        if (!hash)
        {
            hash = cast(size_t)cast(void*)enclosing;
            hash += arrayObjectHash(&tdtypes);
            hash += hash == 0;
        }
        return hash;
    }

    /***********************************************
     * Returns true if this is not instantiated in non-root module, and
     * is a part of non-speculative instantiatiation.
     *
     * Note: minst does not stabilize until semantic analysis is completed,
     * so don't call this function during semantic analysis to return precise result.
     */
    final bool needsCodegen()
    {
        // Now -allInst is just for the backward compatibility.
        if (global.params.allInst)
        {
            //printf("%s minst = %s, enclosing (%s).isNonRoot = %d\n",
            //    toPrettyChars(), minst ? minst.toChars() : NULL,
            //    enclosing ? enclosing.toPrettyChars() : NULL, enclosing && enclosing.inNonRoot());
            if (enclosing)
            {
                /* https://issues.dlang.org/show_bug.cgi?id=14588
                 * If the captured context is not a function
                 * (e.g. class), the instance layout determination is guaranteed,
                 * because the semantic/semantic2 pass will be executed
                 * even for non-root instances.
                 */
                if (!enclosing.isFuncDeclaration())
                    return true;

                /* https://issues.dlang.org/show_bug.cgi?id=14834
                 * If the captured context is a function,
                 * this excessive instantiation may cause ODR violation, because
                 * -allInst and others doesn't guarantee the semantic3 execution
                 * for that function.
                 *
                 * If the enclosing is also an instantiated function,
                 * we have to rely on the ancestor's needsCodegen() result.
                 */
                if (TemplateInstance ti = enclosing.isInstantiated())
                    return ti.needsCodegen();

                /* https://issues.dlang.org/show_bug.cgi?id=13415
                 * If and only if the enclosing scope needs codegen,
                 * this nested templates would also need code generation.
                 */
                return !enclosing.inNonRoot();
            }
            return true;
        }

        if (!minst)
        {
            // If this is a speculative instantiation,
            // 1. do codegen if ancestors really needs codegen.
            // 2. become non-speculative if siblings are not speculative

            TemplateInstance tnext = this.tnext;
            TemplateInstance tinst = this.tinst;
            // At first, disconnect chain first to prevent infinite recursion.
            this.tnext = null;
            this.tinst = null;

            // Determine necessity of tinst before tnext.
            if (tinst && tinst.needsCodegen())
            {
                minst = tinst.minst; // cache result
                assert(minst);
                assert(minst.isRoot() || minst.rootImports());
                return true;
            }
            if (tnext && (tnext.needsCodegen() || tnext.minst))
            {
                minst = tnext.minst; // cache result
                assert(minst);
                return minst.isRoot() || minst.rootImports();
            }

            // Elide codegen because this is really speculative.
            return false;
        }

        /* Even when this is reached to the codegen pass,
         * a non-root nested template should not generate code,
         * due to avoid ODR violation.
         */
        if (enclosing && enclosing.inNonRoot())
        {
            if (tinst)
            {
                auto r = tinst.needsCodegen();
                minst = tinst.minst; // cache result
                return r;
            }
            if (tnext)
            {
                auto r = tnext.needsCodegen();
                minst = tnext.minst; // cache result
                return r;
            }
            return false;
        }

        /* The issue is that if the importee is compiled with a different -debug
         * setting than the importer, the importer may believe it exists
         * in the compiled importee when it does not, when the instantiation
         * is behind a conditional debug declaration.
         */
        // workaround for https://issues.dlang.org/show_bug.cgi?id=11239
        if (global.params.useUnitTests ||
            global.params.debuglevel)
        {
            // Prefer instantiations from root modules, to maximize link-ability.
            if (minst.isRoot())
                return true;

            TemplateInstance tnext = this.tnext;
            TemplateInstance tinst = this.tinst;
            this.tnext = null;
            this.tinst = null;

            if (tinst && tinst.needsCodegen())
            {
                minst = tinst.minst; // cache result
                assert(minst);
                assert(minst.isRoot() || minst.rootImports());
                return true;
            }
            if (tnext && tnext.needsCodegen())
            {
                minst = tnext.minst; // cache result
                assert(minst);
                assert(minst.isRoot() || minst.rootImports());
                return true;
            }

            // https://issues.dlang.org/show_bug.cgi?id=2500 case
            if (minst.rootImports())
                return true;

            // Elide codegen because this is not included in root instances.
            return false;
        }
        else
        {
            // Prefer instantiations from non-root module, to minimize object code size.

            /* If a TemplateInstance is ever instantiated by non-root modules,
             * we do not have to generate code for it,
             * because it will be generated when the non-root module is compiled.
             *
             * But, if the non-root 'minst' imports any root modules, it might still need codegen.
             *
             * The problem is if A imports B, and B imports A, and both A
             * and B instantiate the same template, does the compilation of A
             * or the compilation of B do the actual instantiation?
             *
             * See https://issues.dlang.org/show_bug.cgi?id=2500.
             */
            if (!minst.isRoot() && !minst.rootImports())
                return false;

            TemplateInstance tnext = this.tnext;
            this.tnext = null;

            if (tnext && !tnext.needsCodegen() && tnext.minst)
            {
                minst = tnext.minst; // cache result
                assert(!minst.isRoot());
                return false;
            }

            // Do codegen because this is not included in non-root instances.
            return true;
        }
    }

    /**********************************************
     * Find template declaration corresponding to template instance.
     *
     * Returns:
     *      false if finding fails.
     * Note:
     *      This function is reentrant against error occurrence. If returns false,
     *      any members of this object won't be modified, and repetition call will
     *      reproduce same error.
     */
    final bool findTempDecl(Scope* sc, WithScopeSymbol* pwithsym)
    {
        if (pwithsym)
            *pwithsym = null;

        if (havetempdecl)
            return true;

        //printf("TemplateInstance.findTempDecl() %s\n", toChars());
        if (!tempdecl)
        {
            /* Given:
             *    foo!( ... )
             * figure out which TemplateDeclaration foo refers to.
             */
            Identifier id = name;
            Dsymbol scopesym;
            Dsymbol s = sc.search(loc, id, &scopesym);
            if (!s)
            {
                s = sc.search_correct(id);
                if (s)
                    error("template '%s' is not defined, did you mean %s?", id.toChars(), s.toChars());
                else
                    error("template '%s' is not defined", id.toChars());
                return false;
            }
            static if (LOG)
            {
                printf("It's an instance of '%s' kind '%s'\n", s.toChars(), s.kind());
                if (s.parent)
                    printf("s.parent = '%s'\n", s.parent.toChars());
            }
            if (pwithsym)
                *pwithsym = scopesym.isWithScopeSymbol();

            /* We might have found an alias within a template when
             * we really want the template.
             */
            TemplateInstance ti;
            if (s.parent && (ti = s.parent.isTemplateInstance()) !is null)
            {
                if (ti.tempdecl && ti.tempdecl.ident == id)
                {
                    /* This is so that one can refer to the enclosing
                     * template, even if it has the same name as a member
                     * of the template, if it has a !(arguments)
                     */
                    TemplateDeclaration td = ti.tempdecl.isTemplateDeclaration();
                    assert(td);
                    if (td.overroot) // if not start of overloaded list of TemplateDeclaration's
                        td = td.overroot; // then get the start
                    s = td;
                }
            }

            if (!updateTempDecl(sc, s))
            {
                return false;
            }
        }
        assert(tempdecl);

        // Look for forward references
        auto tovers = tempdecl.isOverloadSet();
        foreach (size_t oi; 0 .. tovers ? tovers.a.dim : 1)
        {
            Dsymbol dstart = tovers ? tovers.a[oi] : tempdecl;
            int r = overloadApply(dstart, (Dsymbol s)
            {
                auto td = s.isTemplateDeclaration();
                if (!td)
                    return 0;

                if (td.semanticRun == PASSinit)
                {
                    if (td._scope)
                    {
                        // Try to fix forward reference. Ungag errors while doing so.
                        Ungag ungag = td.ungagSpeculative();
                        td.semantic(td._scope);
                    }
                    if (td.semanticRun == PASSinit)
                    {
                        error("%s forward references template declaration %s",
                            toChars(), td.toChars());
                        return 1;
                    }
                }
                return 0;
            });
            if (r)
                return false;
        }
        return true;
    }

    /**********************************************
     * Confirm s is a valid template, then store it.
     * Input:
     *      sc
     *      s   candidate symbol of template. It may be:
     *          TemplateDeclaration
     *          FuncDeclaration with findTemplateDeclRoot() != NULL
     *          OverloadSet which contains candidates
     * Returns:
     *      true if updating succeeds.
     */
    final bool updateTempDecl(Scope* sc, Dsymbol s)
    {
        if (s)
        {
            Identifier id = name;
            s = s.toAlias();

            /* If an OverloadSet, look for a unique member that is a template declaration
             */
            OverloadSet os = s.isOverloadSet();
            if (os)
            {
                s = null;
                for (size_t i = 0; i < os.a.dim; i++)
                {
                    Dsymbol s2 = os.a[i];
                    if (FuncDeclaration f = s2.isFuncDeclaration())
                        s2 = f.findTemplateDeclRoot();
                    else
                        s2 = s2.isTemplateDeclaration();
                    if (s2)
                    {
                        if (s)
                        {
                            tempdecl = os;
                            return true;
                        }
                        s = s2;
                    }
                }
                if (!s)
                {
                    error("template '%s' is not defined", id.toChars());
                    return false;
                }
            }

            OverDeclaration od = s.isOverDeclaration();
            if (od)
            {
                tempdecl = od; // TODO: more strict check
                return true;
            }

            /* It should be a TemplateDeclaration, not some other symbol
             */
            if (FuncDeclaration f = s.isFuncDeclaration())
                tempdecl = f.findTemplateDeclRoot();
            else
                tempdecl = s.isTemplateDeclaration();
            if (!tempdecl)
            {
                if (!s.parent && global.errors)
                    return false;
                if (!s.parent && s.getType())
                {
                    Dsymbol s2 = s.getType().toDsymbol(sc);
                    if (!s2)
                    {
                        error("%s is not a template declaration, it is a %s", id.toChars(), s.kind());
                        return false;
                    }
                    s = s2;
                }
                debug
                {
                    //if (!s.parent) printf("s = %s %s\n", s.kind(), s.toChars());
                }
                //assert(s.parent);
                TemplateInstance ti = s.parent ? s.parent.isTemplateInstance() : null;
                if (ti && (ti.name == s.ident || ti.toAlias().ident == s.ident) && ti.tempdecl)
                {
                    /* This is so that one can refer to the enclosing
                     * template, even if it has the same name as a member
                     * of the template, if it has a !(arguments)
                     */
                    TemplateDeclaration td = ti.tempdecl.isTemplateDeclaration();
                    assert(td);
                    if (td.overroot) // if not start of overloaded list of TemplateDeclaration's
                        td = td.overroot; // then get the start
                    tempdecl = td;
                }
                else
                {
                    error("%s is not a template declaration, it is a %s", id.toChars(), s.kind());
                    return false;
                }
            }
        }
        return (tempdecl !is null);
    }

    /**********************************
     * Run semantic of tiargs as arguments of template.
     * Input:
     *      loc
     *      sc
     *      tiargs  array of template arguments
     *      flags   1: replace const variables with their initializers
     *              2: don't devolve Parameter to Type
     * Returns:
     *      false if one or more arguments have errors.
     */
    static bool semanticTiargs(Loc loc, Scope* sc, Objects* tiargs, int flags)
    {
        // Run semantic on each argument, place results in tiargs[]
        //printf("+TemplateInstance.semanticTiargs()\n");
        if (!tiargs)
            return true;
        bool err = false;
        for (size_t j = 0; j < tiargs.dim; j++)
        {
            RootObject o = (*tiargs)[j];
            Type ta = isType(o);
            Expression ea = isExpression(o);
            Dsymbol sa = isDsymbol(o);

            //printf("1: (*tiargs)[%d] = %p, s=%p, v=%p, ea=%p, ta=%p\n", j, o, isDsymbol(o), isTuple(o), ea, ta);
            if (ta)
            {
                //printf("type %s\n", ta.toChars());
                // It might really be an Expression or an Alias
                ta.resolve(loc, sc, &ea, &ta, &sa);
                if (ea)
                    goto Lexpr;
                if (sa)
                    goto Ldsym;
                if (ta is null)
                {
                    assert(global.errors);
                    ta = Type.terror;
                }

            Ltype:
                if (ta.ty == Ttuple)
                {
                    // Expand tuple
                    TypeTuple tt = cast(TypeTuple)ta;
                    size_t dim = tt.arguments.dim;
                    tiargs.remove(j);
                    if (dim)
                    {
                        tiargs.reserve(dim);
                        for (size_t i = 0; i < dim; i++)
                        {
                            Parameter arg = (*tt.arguments)[i];
                            if (flags & 2 && arg.ident)
                                tiargs.insert(j + i, arg);
                            else
                                tiargs.insert(j + i, arg.type);
                        }
                    }
                    j--;
                    continue;
                }
                if (ta.ty == Terror)
                {
                    err = true;
                    continue;
                }
                (*tiargs)[j] = ta.merge2();
            }
            else if (ea)
            {
            Lexpr:
                //printf("+[%d] ea = %s %s\n", j, Token.toChars(ea.op), ea.toChars());
                if (flags & 1) // only used by __traits
                {
                    ea = ea.semantic(sc);

                    // must not interpret the args, excepting template parameters
                    if (ea.op != TOKvar || ((cast(VarExp)ea).var.storage_class & STCtemplateparameter))
                    {
                        ea = ea.optimize(WANTvalue);
                    }
                }
                else
                {
                    sc = sc.startCTFE();
                    ea = ea.semantic(sc);
                    sc = sc.endCTFE();

                    if (ea.op == TOKvar)
                    {
                        /* This test is to skip substituting a const var with
                         * its initializer. The problem is the initializer won't
                         * match with an 'alias' parameter. Instead, do the
                         * const substitution in TemplateValueParameter.matchArg().
                         */
                    }
                    else if (definitelyValueParameter(ea))
                    {
                        if (ea.checkValue()) // check void expression
                            ea = new ErrorExp();
                        uint olderrs = global.errors;
                        ea = ea.ctfeInterpret();
                        if (global.errors != olderrs)
                            ea = new ErrorExp();
                    }
                }
                //printf("-[%d] ea = %s %s\n", j, Token.toChars(ea.op), ea.toChars());
                if (ea.op == TOKtuple)
                {
                    // Expand tuple
                    TupleExp te = cast(TupleExp)ea;
                    size_t dim = te.exps.dim;
                    tiargs.remove(j);
                    if (dim)
                    {
                        tiargs.reserve(dim);
                        for (size_t i = 0; i < dim; i++)
                            tiargs.insert(j + i, (*te.exps)[i]);
                    }
                    j--;
                    continue;
                }
                if (ea.op == TOKerror)
                {
                    err = true;
                    continue;
                }
                (*tiargs)[j] = ea;

                if (ea.op == TOKtype)
                {
                    ta = ea.type;
                    goto Ltype;
                }
                if (ea.op == TOKscope)
                {
                    sa = (cast(ScopeExp)ea).sds;
                    goto Ldsym;
                }
                if (ea.op == TOKfunction)
                {
                    FuncExp fe = cast(FuncExp)ea;
                    /* A function literal, that is passed to template and
                     * already semanticed as function pointer, never requires
                     * outer frame. So convert it to global function is valid.
                     */
                    if (fe.fd.tok == TOKreserved && fe.type.ty == Tpointer)
                    {
                        // change to non-nested
                        fe.fd.tok = TOKfunction;
                        fe.fd.vthis = null;
                    }
                    else if (fe.td)
                    {
                        /* If template argument is a template lambda,
                         * get template declaration itself. */
                        //sa = fe.td;
                        //goto Ldsym;
                    }
                }
                if (ea.op == TOKdotvar)
                {
                    // translate expression to dsymbol.
                    sa = (cast(DotVarExp)ea).var;
                    goto Ldsym;
                }
                if (ea.op == TOKtemplate)
                {
                    sa = (cast(TemplateExp)ea).td;
                    goto Ldsym;
                }
                if (ea.op == TOKdottd)
                {
                    // translate expression to dsymbol.
                    sa = (cast(DotTemplateExp)ea).td;
                    goto Ldsym;
                }
            }
            else if (sa)
            {
            Ldsym:
                //printf("dsym %s %s\n", sa.kind(), sa.toChars());
                if (sa.errors)
                {
                    err = true;
                    continue;
                }

                TupleDeclaration d = sa.toAlias().isTupleDeclaration();
                if (d)
                {
                    // Expand tuple
                    tiargs.remove(j);
                    tiargs.insert(j, d.objects);
                    j--;
                    continue;
                }
                if (FuncAliasDeclaration fa = sa.isFuncAliasDeclaration())
                {
                    FuncDeclaration f = fa.toAliasFunc();
                    if (!fa.hasOverloads && f.isUnique())
                    {
                        // Strip FuncAlias only when the aliased function
                        // does not have any overloads.
                        sa = f;
                    }
                }
                (*tiargs)[j] = sa;

                TemplateDeclaration td = sa.isTemplateDeclaration();
                if (td && td.semanticRun == PASSinit && td.literal)
                {
                    td.semantic(sc);
                }
                FuncDeclaration fd = sa.isFuncDeclaration();
                if (fd)
                    fd.functionSemantic();
            }
            else if (isParameter(o))
            {
            }
            else
            {
                assert(0);
            }
            //printf("1: (*tiargs)[%d] = %p\n", j, (*tiargs)[j]);
        }
        version (none)
        {
            printf("-TemplateInstance.semanticTiargs()\n");
            for (size_t j = 0; j < tiargs.dim; j++)
            {
                RootObject o = (*tiargs)[j];
                Type ta = isType(o);
                Expression ea = isExpression(o);
                Dsymbol sa = isDsymbol(o);
                Tuple va = isTuple(o);
                printf("\ttiargs[%d] = ta %p, ea %p, sa %p, va %p\n", j, ta, ea, sa, va);
            }
        }
        return !err;
    }

    /**********************************
     * Run semantic on the elements of tiargs.
     * Input:
     *      sc
     * Returns:
     *      false if one or more arguments have errors.
     * Note:
     *      This function is reentrant against error occurrence. If returns false,
     *      all elements of tiargs won't be modified.
     */
    final bool semanticTiargs(Scope* sc)
    {
        //printf("+TemplateInstance.semanticTiargs() %s\n", toChars());
        if (semantictiargsdone)
            return true;
        if (semanticTiargs(loc, sc, tiargs, 0))
        {
            // cache the result iff semantic analysis succeeded entirely
            semantictiargsdone = 1;
            return true;
        }
        return false;
    }

    final bool findBestMatch(Scope* sc, Expressions* fargs)
    {
        if (havetempdecl)
        {
            TemplateDeclaration tempdecl = this.tempdecl.isTemplateDeclaration();
            assert(tempdecl);
            assert(tempdecl._scope);
            // Deduce tdtypes
            tdtypes.setDim(tempdecl.parameters.dim);
            if (!tempdecl.matchWithInstance(sc, this, &tdtypes, fargs, 2))
            {
                error("incompatible arguments for template instantiation");
                return false;
            }
            // TODO: Normalizing tiargs for https://issues.dlang.org/show_bug.cgi?id=7469 is necessary?
            return true;
        }

        static if (LOG)
        {
            printf("TemplateInstance.findBestMatch()\n");
        }

        uint errs = global.errors;
        TemplateDeclaration td_last = null;
        Objects dedtypes;

        /* Since there can be multiple TemplateDeclaration's with the same
         * name, look for the best match.
         */
        auto tovers = tempdecl.isOverloadSet();
        foreach (size_t oi; 0 .. tovers ? tovers.a.dim : 1)
        {
            TemplateDeclaration td_best;
            TemplateDeclaration td_ambig;
            MATCH m_best = MATCHnomatch;

            Dsymbol dstart = tovers ? tovers.a[oi] : tempdecl;
            overloadApply(dstart, (Dsymbol s)
            {
                auto  td = s.isTemplateDeclaration();
                if (!td || td == td_best)   // skip duplicates
                    return 0;

                //printf("td = %s\n", td.toPrettyChars());
                // If more arguments than parameters,
                // then this is no match.
                if (td.parameters.dim < tiargs.dim)
                {
                    if (!td.isVariadic())
                        return 0;
                }

                dedtypes.setDim(td.parameters.dim);
                dedtypes.zero();
                assert(td.semanticRun != PASSinit);

                MATCH m = td.matchWithInstance(sc, this, &dedtypes, fargs, 0);
                //printf("matchWithInstance = %d\n", m);
                if (m <= MATCHnomatch) // no match at all
                    return 0;
                if (m < m_best) goto Ltd_best;
                if (m > m_best) goto Ltd;

                // Disambiguate by picking the most specialized TemplateDeclaration
                {
                MATCH c1 = td.leastAsSpecialized(sc, td_best, fargs);
                MATCH c2 = td_best.leastAsSpecialized(sc, td, fargs);
                //printf("c1 = %d, c2 = %d\n", c1, c2);
                if (c1 > c2) goto Ltd;
                if (c1 < c2) goto Ltd_best;
                }

                td_ambig = td;
                return 0;

            Ltd_best:
                // td_best is the best match so far
                td_ambig = null;
                return 0;

            Ltd:
                // td is the new best match
                td_ambig = null;
                td_best = td;
                m_best = m;
                tdtypes.setDim(dedtypes.dim);
                memcpy(tdtypes.tdata(), dedtypes.tdata(), tdtypes.dim * (void*).sizeof);
                return 0;
            });

            if (td_ambig)
            {
                .error(loc, "%s %s.%s matches more than one template declaration:\n%s:     %s\nand\n%s:     %s",
                    td_best.kind(), td_best.parent.toPrettyChars(), td_best.ident.toChars(),
                    td_best.loc.toChars(), td_best.toChars(),
                    td_ambig.loc.toChars(), td_ambig.toChars());
                return false;
            }
            if (td_best)
            {
                if (!td_last)
                    td_last = td_best;
                else if (td_last != td_best)
                {
                    ScopeDsymbol.multiplyDefined(loc, td_last, td_best);
                    return false;
                }
            }
        }

        if (td_last)
        {
            /* https://issues.dlang.org/show_bug.cgi?id=7469
             * Normalize tiargs by using corresponding deduced
             * template value parameters and tuples for the correct mangling.
             *
             * By doing this before hasNestedArgs, CTFEable local variable will be
             * accepted as a value parameter. For example:
             *
             *  void foo() {
             *    struct S(int n) {}   // non-global template
             *    const int num = 1;   // CTFEable local variable
             *    S!num s;             // S!1 is instantiated, not S!num
             *  }
             */
            size_t dim = td_last.parameters.dim - (td_last.isVariadic() ? 1 : 0);
            for (size_t i = 0; i < dim; i++)
            {
                if (tiargs.dim <= i)
                    tiargs.push(tdtypes[i]);
                assert(i < tiargs.dim);

                auto tvp = (*td_last.parameters)[i].isTemplateValueParameter();
                if (!tvp)
                    continue;
                assert(tdtypes[i]);
                // tdtypes[i] is already normalized to the required type in matchArg

                (*tiargs)[i] = tdtypes[i];
            }
            if (td_last.isVariadic() && tiargs.dim == dim && tdtypes[dim])
            {
                Tuple va = isTuple(tdtypes[dim]);
                assert(va);
                for (size_t i = 0; i < va.objects.dim; i++)
                    tiargs.push(va.objects[i]);
            }
        }
        else if (errors && inst)
        {
            // instantiation was failed with error reporting
            assert(global.errors);
            return false;
        }
        else
        {
            auto tdecl = tempdecl.isTemplateDeclaration();

            if (errs != global.errors)
                errorSupplemental(loc, "while looking for match for %s", toChars());
            else if (tdecl && !tdecl.overnext)
            {
                // Only one template, so we can give better error message
                error("does not match template declaration %s", tdecl.toChars());
            }
            else
                .error(loc, "%s %s.%s does not match any template declaration", tempdecl.kind(), tempdecl.parent.toPrettyChars(), tempdecl.ident.toChars());
            return false;
        }

        /* The best match is td_last
         */
        tempdecl = td_last;

        static if (LOG)
        {
            printf("\tIt's a match with template declaration '%s'\n", tempdecl.toChars());
        }
        return (errs == global.errors);
    }

    /*****************************************************
     * Determine if template instance is really a template function,
     * and that template function needs to infer types from the function
     * arguments.
     *
     * Like findBestMatch, iterate possible template candidates,
     * but just looks only the necessity of type inference.
     */
    final bool needsTypeInference(Scope* sc, int flag = 0)
    {
        //printf("TemplateInstance.needsTypeInference() %s\n", toChars());
        if (semanticRun != PASSinit)
            return false;

        uint olderrs = global.errors;
        Objects dedtypes;
        size_t count = 0;

        auto tovers = tempdecl.isOverloadSet();
        foreach (size_t oi; 0 .. tovers ? tovers.a.dim : 1)
        {
            Dsymbol dstart = tovers ? tovers.a[oi] : tempdecl;
            int r = overloadApply(dstart, (Dsymbol s)
            {
                auto td = s.isTemplateDeclaration();
                if (!td)
                    return 0;

                /* If any of the overloaded template declarations need inference,
                 * then return true
                 */
                if (!td.onemember)
                    return 0;
                if (auto td2 = td.onemember.isTemplateDeclaration())
                {
                    if (!td2.onemember || !td2.onemember.isFuncDeclaration())
                        return 0;
                    if (tiargs.dim >= td.parameters.dim - (td.isVariadic() ? 1 : 0))
                        return 0;
                    return 1;
                }
                auto fd = td.onemember.isFuncDeclaration();
                if (!fd || fd.type.ty != Tfunction)
                    return 0;

                foreach (tp; *td.parameters)
                {
                    if (tp.isTemplateThisParameter())
                        return 1;
                }

                /* Determine if the instance arguments, tiargs, are all that is necessary
                 * to instantiate the template.
                 */
                //printf("tp = %p, td.parameters.dim = %d, tiargs.dim = %d\n", tp, td.parameters.dim, tiargs.dim);
                auto tf = cast(TypeFunction)fd.type;
                if (size_t dim = Parameter.dim(tf.parameters))
                {
                    auto tp = td.isVariadic();
                    if (tp && td.parameters.dim > 1)
                        return 1;

                    if (!tp && tiargs.dim < td.parameters.dim)
                    {
                        // Can remain tiargs be filled by default arguments?
                        foreach (size_t i; tiargs.dim .. td.parameters.dim)
                        {
                            if (!(*td.parameters)[i].hasDefaultArg())
                                return 1;
                        }
                    }

                    foreach (size_t i; 0 .. dim)
                    {
                        // 'auto ref' needs inference.
                        if (Parameter.getNth(tf.parameters, i).storageClass & STCauto)
                            return 1;
                    }
                }

                if (!flag)
                {
                    /* Calculate the need for overload resolution.
                     * When only one template can match with tiargs, inference is not necessary.
                     */
                    dedtypes.setDim(td.parameters.dim);
                    dedtypes.zero();
                    if (td.semanticRun == PASSinit)
                    {
                        if (td._scope)
                        {
                            // Try to fix forward reference. Ungag errors while doing so.
                            Ungag ungag = td.ungagSpeculative();
                            td.semantic(td._scope);
                        }
                        if (td.semanticRun == PASSinit)
                        {
                            error("%s forward references template declaration %s", toChars(), td.toChars());
                            return 1;
                        }
                    }
                    MATCH m = td.matchWithInstance(sc, this, &dedtypes, null, 0);
                    if (m <= MATCHnomatch)
                        return 0;
                }

                /* If there is more than one function template which matches, we may
                 * need type inference (see https://issues.dlang.org/show_bug.cgi?id=4430)
                 */
                return ++count > 1 ? 1 : 0;
            });
            if (r)
                return true;
        }

        if (olderrs != global.errors)
        {
            if (!global.gag)
            {
                errorSupplemental(loc, "while looking for match for %s", toChars());
                semanticRun = PASSsemanticdone;
                inst = this;
            }
            errors = true;
        }
        //printf("false\n");
        return false;
    }

    /*****************************************
     * Determines if a TemplateInstance will need a nested
     * generation of the TemplateDeclaration.
     * Sets enclosing property if so, and returns != 0;
     */
    final bool hasNestedArgs(Objects* args, bool isstatic)
    {
        int nested = 0;
        //printf("TemplateInstance.hasNestedArgs('%s')\n", tempdecl.ident.toChars());

        version (none)
        {
            if (!enclosing)
            {
                if (TemplateInstance ti = tempdecl.isInstantiated())
                    enclosing = ti.enclosing;
            }
        }

        /* A nested instance happens when an argument references a local
         * symbol that is on the stack.
         */
        for (size_t i = 0; i < args.dim; i++)
        {
            RootObject o = (*args)[i];
            Expression ea = isExpression(o);
            Dsymbol sa = isDsymbol(o);
            Tuple va = isTuple(o);
            if (ea)
            {
                if (ea.op == TOKvar)
                {
                    sa = (cast(VarExp)ea).var;
                    goto Lsa;
                }
                if (ea.op == TOKthis)
                {
                    sa = (cast(ThisExp)ea).var;
                    goto Lsa;
                }
                if (ea.op == TOKfunction)
                {
                    if ((cast(FuncExp)ea).td)
                        sa = (cast(FuncExp)ea).td;
                    else
                        sa = (cast(FuncExp)ea).fd;
                    goto Lsa;
                }
                // Emulate Expression.toMangleBuffer call that had exist in TemplateInstance.genIdent.
                if (ea.op != TOKint64 && ea.op != TOKfloat64 && ea.op != TOKcomplex80 && ea.op != TOKnull && ea.op != TOKstring && ea.op != TOKarrayliteral && ea.op != TOKassocarrayliteral && ea.op != TOKstructliteral)
                {
                    ea.error("expression %s is not a valid template value argument", ea.toChars());
                    errors = true;
                }
            }
            else if (sa)
            {
            Lsa:
                sa = sa.toAlias();
                TemplateDeclaration td = sa.isTemplateDeclaration();
                if (td)
                {
                    TemplateInstance ti = sa.toParent().isTemplateInstance();
                    if (ti && ti.enclosing)
                        sa = ti;
                }
                TemplateInstance ti = sa.isTemplateInstance();
                Declaration d = sa.isDeclaration();
                if ((td && td.literal) || (ti && ti.enclosing) || (d && !d.isDataseg() && !(d.storage_class & STCmanifest) && (!d.isFuncDeclaration() || d.isFuncDeclaration().isNested()) && !isTemplateMixin()))
                {
                    // if module level template
                    if (isstatic)
                    {
                        Dsymbol dparent = sa.toParent2();
                        if (!enclosing)
                            enclosing = dparent;
                        else if (enclosing != dparent)
                        {
                            /* Select the more deeply nested of the two.
                             * Error if one is not nested inside the other.
                             */
                            for (Dsymbol p = enclosing; p; p = p.parent)
                            {
                                if (p == dparent)
                                    goto L1; // enclosing is most nested
                            }
                            for (Dsymbol p = dparent; p; p = p.parent)
                            {
                                if (p == enclosing)
                                {
                                    enclosing = dparent;
                                    goto L1; // dparent is most nested
                                }
                            }
                            error("%s is nested in both %s and %s", toChars(), enclosing.toChars(), dparent.toChars());
                            errors = true;
                        }
                    L1:
                        //printf("\tnested inside %s\n", enclosing.toChars());
                        nested |= 1;
                    }
                    else
                    {
                        error("cannot use local '%s' as parameter to non-global template %s", sa.toChars(), tempdecl.toChars());
                        errors = true;
                    }
                }
            }
            else if (va)
            {
                nested |= cast(int)hasNestedArgs(&va.objects, isstatic);
            }
        }
        //printf("-TemplateInstance.hasNestedArgs('%s') = %d\n", tempdecl.ident.toChars(), nested);
        return nested != 0;
    }

    /*****************************************
     * Append 'this' to the specific module members[]
     */
    final Dsymbols* appendToModuleMember()
    {
        Module mi = minst; // instantiated . inserted module

        if (global.params.useUnitTests || global.params.debuglevel)
        {
            // Turn all non-root instances to speculative
            if (mi && !mi.isRoot())
                mi = null;
        }

        //printf("%s.appendToModuleMember() enclosing = %s mi = %s\n",
        //    toPrettyChars(),
        //    enclosing ? enclosing.toPrettyChars() : null,
        //    mi ? mi.toPrettyChars() : null);
        if (!mi || mi.isRoot())
        {
            /* If the instantiated module is speculative or root, insert to the
             * member of a root module. Then:
             *  - semantic3 pass will get called on the instance members.
             *  - codegen pass will get a selection chance to do/skip it.
             */
            static Dsymbol getStrictEnclosing(TemplateInstance ti)
            {
                do
                {
                    if (ti.enclosing)
                        return ti.enclosing;
                    ti = ti.tempdecl.isInstantiated();
                } while (ti);
                return null;
            }

            Dsymbol enc = getStrictEnclosing(this);
            // insert target is made stable by using the module
            // where tempdecl is declared.
            mi = (enc ? enc : tempdecl).getModule();
            if (!mi.isRoot())
                mi = mi.importedFrom;
            assert(mi.isRoot());
        }
        else
        {
            /* If the instantiated module is non-root, insert to the member of the
             * non-root module. Then:
             *  - semantic3 pass won't be called on the instance.
             *  - codegen pass won't reach to the instance.
             */
        }
        //printf("\t-. mi = %s\n", mi.toPrettyChars());

        if (memberOf is mi)     // already a member
        {
            debug               // make sure it really is a member
            {
                auto a = mi.members;
                for (size_t i = 0; 1; ++i)
                {
                    assert(i != a.dim);
                    if (this == (*a)[i])
                        break;
                }
            }
            return null;
        }

        Dsymbols* a = mi.members;
        a.push(this);
        memberOf = mi;
        if (mi.semanticRun >= PASSsemantic2done && mi.isRoot())
            Module.addDeferredSemantic2(this);
        if (mi.semanticRun >= PASSsemantic3done && mi.isRoot())
            Module.addDeferredSemantic3(this);
        return a;
    }

    /****************************************************
     * Declare parameters of template instance, initialize them with the
     * template instance arguments.
     */
    final void declareParameters(Scope* sc)
    {
        TemplateDeclaration tempdecl = this.tempdecl.isTemplateDeclaration();
        assert(tempdecl);

        //printf("TemplateInstance.declareParameters()\n");
        for (size_t i = 0; i < tdtypes.dim; i++)
        {
            TemplateParameter tp = (*tempdecl.parameters)[i];
            //RootObject *o = (*tiargs)[i];
            RootObject o = tdtypes[i]; // initializer for tp

            //printf("\ttdtypes[%d] = %p\n", i, o);
            tempdecl.declareParameter(sc, tp, o);
        }
    }

    /****************************************
     * This instance needs an identifier for name mangling purposes.
     * Create one by taking the template declaration name and adding
     * the type signature for it.
     */
    final Identifier genIdent(Objects* args)
    {
        TemplateDeclaration tempdecl = this.tempdecl.isTemplateDeclaration();
        assert(tempdecl);

        //printf("TemplateInstance.genIdent('%s')\n", tempdecl.ident.toChars());
        OutBuffer buf;

        const id = tempdecl.ident.toString();
        // Use "__U" for the symbols declared inside template constraint.
        const char T = members ? 'T' : 'U';
        buf.printf("__%c%u%.*s", T, cast(int)id.length, cast(int)id.length, id.ptr);

        size_t nparams = tempdecl.parameters.dim - (tempdecl.isVariadic() ? 1 : 0);
        for (size_t i = 0; i < args.dim; i++)
        {
            RootObject o = (*args)[i];
            Type ta = isType(o);
            Expression ea = isExpression(o);
            Dsymbol sa = isDsymbol(o);
            Tuple va = isTuple(o);
            //printf("\to [%d] %p ta %p ea %p sa %p va %p\n", i, o, ta, ea, sa, va);
            if (i < nparams && (*tempdecl.parameters)[i].specialization())
                buf.writeByte('H'); // https://issues.dlang.org/show_bug.cgi?id=6574
            if (ta)
            {
                buf.writeByte('T');
                if (ta.deco)
                    buf.writestring(ta.deco);
                else
                {
                    debug
                    {
                        if (!global.errors)
                            printf("ta = %d, %s\n", ta.ty, ta.toChars());
                    }
                    assert(global.errors);
                }
            }
            else if (ea)
            {
                // Don't interpret it yet, it might actually be an alias
                ea = ea.optimize(WANTvalue);
                if (ea.op == TOKvar)
                {
                    sa = (cast(VarExp)ea).var;
                    ea = null;
                    goto Lsa;
                }
                if (ea.op == TOKthis)
                {
                    sa = (cast(ThisExp)ea).var;
                    ea = null;
                    goto Lsa;
                }
                if (ea.op == TOKfunction)
                {
                    if ((cast(FuncExp)ea).td)
                        sa = (cast(FuncExp)ea).td;
                    else
                        sa = (cast(FuncExp)ea).fd;
                    ea = null;
                    goto Lsa;
                }
                buf.writeByte('V');
                if (ea.op == TOKtuple)
                {
                    ea.error("tuple is not a valid template value argument");
                    continue;
                }
                // Now that we know it is not an alias, we MUST obtain a value
                uint olderr = global.errors;
                ea = ea.ctfeInterpret();
                if (ea.op == TOKerror || olderr != global.errors)
                    continue;

                /* Use deco that matches what it would be for a function parameter
                 */
                buf.writestring(ea.type.deco);
                mangleToBuffer(ea, &buf);
            }
            else if (sa)
            {
            Lsa:
                buf.writeByte('S');
                sa = sa.toAlias();
                Declaration d = sa.isDeclaration();
                if (d && (!d.type || !d.type.deco))
                {
                    error("forward reference of %s %s", d.kind(), d.toChars());
                    continue;
                }

                OutBuffer bufsa;
                mangleToBuffer(sa, &bufsa);
                auto s = bufsa.peekSlice();

                /* https://issues.dlang.org/show_bug.cgi?id=3043
                 * If the first character of p is a digit this
                 * causes ambiguity issues because the digits of the two numbers are adjacent.
                 * Current demanglers resolve this by trying various places to separate the
                 * numbers until one gets a successful demangle.
                 * Unfortunately, fixing this ambiguity will break existing binary
                 * compatibility and the demanglers, so we'll leave it as is.
                 */
                buf.printf("%u%.*s", cast(uint)s.length, cast(int)s.length, s.ptr);
            }
            else if (va)
            {
                assert(i + 1 == args.dim); // must be last one
                args = &va.objects;
                i = -cast(size_t)1;
            }
            else
                assert(0);
        }
        buf.writeByte('Z');
        //printf("\tgenIdent = %s\n", buf.peekString());
        return Identifier.idPool(buf.peekSlice());
    }

    final void expandMembers(Scope* sc2)
    {
        for (size_t i = 0; i < members.dim; i++)
        {
            Dsymbol s = (*members)[i];
            s.setScope(sc2);
        }

        for (size_t i = 0; i < members.dim; i++)
        {
            Dsymbol s = (*members)[i];
            s.importAll(sc2);
        }

        for (size_t i = 0; i < members.dim; i++)
        {
            Dsymbol s = (*members)[i];
            //printf("\t[%d] semantic on '%s' %p kind %s in '%s'\n", i, s.toChars(), s, s.kind(), this.toChars());
            //printf("test: enclosing = %d, sc2.parent = %s\n", enclosing, sc2.parent.toChars());
            //if (enclosing)
            //    s.parent = sc.parent;
            //printf("test3: enclosing = %d, s.parent = %s\n", enclosing, s.parent.toChars());
            s.semantic(sc2);
            //printf("test4: enclosing = %d, s.parent = %s\n", enclosing, s.parent.toChars());
            Module.runDeferredSemantic();
        }
    }

    final void tryExpandMembers(Scope* sc2)
    {
        static __gshared int nest;
        // extracted to a function to allow windows SEH to work without destructors in the same function
        //printf("%d\n", nest);
        if (++nest > 500)
        {
            global.gag = 0; // ensure error message gets printed
            error("recursive expansion");
            fatal();
        }

        expandMembers(sc2);

        nest--;
    }

    final void trySemantic3(Scope* sc2)
    {
        // extracted to a function to allow windows SEH to work without destructors in the same function
        static __gshared int nest;
        //printf("%d\n", nest);
        if (++nest > 300)
        {
            global.gag = 0; // ensure error message gets printed
            error("recursive expansion");
            fatal();
        }

        semantic3(sc2);

        --nest;
    }

    override final inout(TemplateInstance) isTemplateInstance() inout
    {
        return this;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/**************************************
 * IsExpression can evaluate the specified type speculatively, and even if
 * it instantiates any symbols, they are normally unnecessary for the
 * final executable.
 * However, if those symbols leak to the actual code, compiler should remark
 * them as non-speculative to generate their code and link to the final executable.
 */
void unSpeculative(Scope* sc, RootObject o)
{
    if (!o)
        return;

    if (Tuple tup = isTuple(o))
    {
        for (size_t i = 0; i < tup.objects.dim; i++)
        {
            unSpeculative(sc, tup.objects[i]);
        }
        return;
    }

    Dsymbol s = getDsymbol(o);
    if (!s)
        return;

    if (Declaration d = s.isDeclaration())
    {
        if (VarDeclaration vd = d.isVarDeclaration())
            o = vd.type;
        else if (AliasDeclaration ad = d.isAliasDeclaration())
        {
            o = ad.getType();
            if (!o)
                o = ad.toAlias();
        }
        else
            o = d.toAlias();

        s = getDsymbol(o);
        if (!s)
            return;
    }

    if (TemplateInstance ti = s.isTemplateInstance())
    {
        // If the instance is already non-speculative,
        // or it is leaked to the speculative scope.
        if (ti.minst !is null || sc.minst is null)
            return;

        // Remark as non-speculative instance.
        ti.minst = sc.minst;
        if (!ti.tinst)
            ti.tinst = sc.tinst;

        unSpeculative(sc, ti.tempdecl);
    }

    if (TemplateInstance ti = s.isInstantiated())
        unSpeculative(sc, ti);
}

/**********************************
 * Return true if e could be valid only as a template value parameter.
 * Return false if it might be an alias or tuple.
 * (Note that even in this case, it could still turn out to be a value).
 */
bool definitelyValueParameter(Expression e)
{
    // None of these can be value parameters
    if (e.op == TOKtuple || e.op == TOKscope ||
        e.op == TOKtype || e.op == TOKdottype ||
        e.op == TOKtemplate || e.op == TOKdottd ||
        e.op == TOKfunction || e.op == TOKerror ||
        e.op == TOKthis || e.op == TOKsuper)
        return false;

    if (e.op != TOKdotvar)
        return true;

    /* Template instantiations involving a DotVar expression are difficult.
     * In most cases, they should be treated as a value parameter, and interpreted.
     * But they might also just be a fully qualified name, which should be treated
     * as an alias.
     */

    // x.y.f cannot be a value
    FuncDeclaration f = (cast(DotVarExp)e).var.isFuncDeclaration();
    if (f)
        return false;

    while (e.op == TOKdotvar)
    {
        e = (cast(DotVarExp)e).e1;
    }
    // this.x.y and super.x.y couldn't possibly be valid values.
    if (e.op == TOKthis || e.op == TOKsuper)
        return false;

    // e.type.x could be an alias
    if (e.op == TOKdottype)
        return false;

    // var.x.y is the only other possible form of alias
    if (e.op != TOKvar)
        return true;

    VarDeclaration v = (cast(VarExp)e).var.isVarDeclaration();
    // func.x.y is not an alias
    if (!v)
        return true;

    // TODO: Should we force CTFE if it is a global constant?
    return false;
}

/***********************************************************
 */
extern (C++) final class TemplateMixin : TemplateInstance
{
    TypeQualified tqual;

    extern (D) this(Loc loc, Identifier ident, TypeQualified tqual, Objects* tiargs)
    {
        super(loc,
              tqual.idents.dim ? cast(Identifier)tqual.idents[tqual.idents.dim - 1] : (cast(TypeIdentifier)tqual).ident,
              tiargs ? tiargs : new Objects());
        //printf("TemplateMixin(ident = '%s')\n", ident ? ident.toChars() : "");
        this.ident = ident;
        this.tqual = tqual;
    }

    override Dsymbol syntaxCopy(Dsymbol s)
    {
        auto tm = new TemplateMixin(loc, ident, cast(TypeQualified)tqual.syntaxCopy(), tiargs);
        return TemplateInstance.syntaxCopy(tm);
    }

    override void semantic(Scope* sc)
    {
        static if (LOG)
        {
            printf("+TemplateMixin.semantic('%s', this=%p)\n", toChars(), this);
            fflush(stdout);
        }
        if (semanticRun != PASSinit)
        {
            // When a class/struct contains mixin members, and is done over
            // because of forward references, never reach here so semanticRun
            // has been reset to PASSinit.
            static if (LOG)
            {
                printf("\tsemantic done\n");
            }
            return;
        }
        semanticRun = PASSsemantic;
        static if (LOG)
        {
            printf("\tdo semantic\n");
        }

        Scope* scx = null;
        if (_scope)
        {
            sc = _scope;
            scx = _scope; // save so we don't make redundant copies
            _scope = null;
        }

        /* Run semantic on each argument, place results in tiargs[],
         * then find best match template with tiargs
         */
        if (!findTempDecl(sc) || !semanticTiargs(sc) || !findBestMatch(sc, null))
        {
            if (semanticRun == PASSinit) // forward reference had occured
            {
                //printf("forward reference - deferring\n");
                _scope = scx ? scx : sc.copy();
                _scope.setNoFree();
                _scope._module.addDeferredSemantic(this);
                return;
            }

            inst = this;
            errors = true;
            return; // error recovery
        }

        auto tempdecl = this.tempdecl.isTemplateDeclaration();
        assert(tempdecl);

        if (!ident)
        {
            /* Assign scope local unique identifier, as same as lambdas.
             */
            const(char)* s = "__mixin";

            DsymbolTable symtab;
            if (FuncDeclaration func = sc.parent.isFuncDeclaration())
            {
                symtab = func.localsymtab;
                if (symtab)
                {
                    // Inside template constraint, symtab is not set yet.
                    goto L1;
                }
            }
            else
            {
                symtab = sc.parent.isScopeDsymbol().symtab;
            L1:
                assert(symtab);
                ident = Identifier.generateId(s, symtab.len + 1);
                symtab.insert(this);
            }
        }

        inst = this;
        parent = sc.parent;

        /* Detect recursive mixin instantiations.
         */
        for (Dsymbol s = parent; s; s = s.parent)
        {
            //printf("\ts = '%s'\n", s.toChars());
            TemplateMixin tm = s.isTemplateMixin();
            if (!tm || tempdecl != tm.tempdecl)
                continue;

            /* Different argument list lengths happen with variadic args
             */
            if (tiargs.dim != tm.tiargs.dim)
                continue;

            for (size_t i = 0; i < tiargs.dim; i++)
            {
                RootObject o = (*tiargs)[i];
                Type ta = isType(o);
                Expression ea = isExpression(o);
                Dsymbol sa = isDsymbol(o);
                RootObject tmo = (*tm.tiargs)[i];
                if (ta)
                {
                    Type tmta = isType(tmo);
                    if (!tmta)
                        goto Lcontinue;
                    if (!ta.equals(tmta))
                        goto Lcontinue;
                }
                else if (ea)
                {
                    Expression tme = isExpression(tmo);
                    if (!tme || !ea.equals(tme))
                        goto Lcontinue;
                }
                else if (sa)
                {
                    Dsymbol tmsa = isDsymbol(tmo);
                    if (sa != tmsa)
                        goto Lcontinue;
                }
                else
                    assert(0);
            }
            error("recursive mixin instantiation");
            return;

        Lcontinue:
            continue;
        }

        // Copy the syntax trees from the TemplateDeclaration
        members = Dsymbol.arraySyntaxCopy(tempdecl.members);
        if (!members)
            return;

        symtab = new DsymbolTable();

        for (Scope* sce = sc; 1; sce = sce.enclosing)
        {
            ScopeDsymbol sds = sce.scopesym;
            if (sds)
            {
                sds.importScope(this, Prot(PROTpublic));
                break;
            }
        }

        static if (LOG)
        {
            printf("\tcreate scope for template parameters '%s'\n", toChars());
        }
        Scope* scy = sc.push(this);
        scy.parent = this;

        argsym = new ScopeDsymbol();
        argsym.parent = scy.parent;
        Scope* argscope = scy.push(argsym);

        uint errorsave = global.errors;

        // Declare each template parameter as an alias for the argument type
        declareParameters(argscope);

        // Add members to enclosing scope, as well as this scope
        for (size_t i = 0; i < members.dim; i++)
        {
            Dsymbol s = (*members)[i];
            s.addMember(argscope, this);
            //printf("sc.parent = %p, sc.scopesym = %p\n", sc.parent, sc.scopesym);
            //printf("s.parent = %s\n", s.parent.toChars());
        }

        // Do semantic() analysis on template instance members
        static if (LOG)
        {
            printf("\tdo semantic() on template instance members '%s'\n", toChars());
        }
        Scope* sc2 = argscope.push(this);
        //size_t deferred_dim = Module.deferred.dim;

        static __gshared int nest;
        //printf("%d\n", nest);
        if (++nest > 500)
        {
            global.gag = 0; // ensure error message gets printed
            error("recursive expansion");
            fatal();
        }

        for (size_t i = 0; i < members.dim; i++)
        {
            Dsymbol s = (*members)[i];
            s.setScope(sc2);
        }

        for (size_t i = 0; i < members.dim; i++)
        {
            Dsymbol s = (*members)[i];
            s.importAll(sc2);
        }

        for (size_t i = 0; i < members.dim; i++)
        {
            Dsymbol s = (*members)[i];
            s.semantic(sc2);
        }

        nest--;

        /* In DeclDefs scope, TemplateMixin does not have to handle deferred symbols.
         * Because the members would already call Module.addDeferredSemantic() for themselves.
         * See Struct, Class, Interface, and EnumDeclaration.semantic().
         */
        //if (!sc.func && Module.deferred.dim > deferred_dim) {}

        AggregateDeclaration ad = toParent().isAggregateDeclaration();
        if (sc.func && !ad)
        {
            semantic2(sc2);
            semantic3(sc2);
        }

        // Give additional context info if error occurred during instantiation
        if (global.errors != errorsave)
        {
            error("error instantiating");
            errors = true;
        }

        sc2.pop();
        argscope.pop();
        scy.pop();

        static if (LOG)
        {
            printf("-TemplateMixin.semantic('%s', this=%p)\n", toChars(), this);
        }
    }

    override void semantic2(Scope* sc)
    {
        if (semanticRun >= PASSsemantic2)
            return;
        semanticRun = PASSsemantic2;
        static if (LOG)
        {
            printf("+TemplateMixin.semantic2('%s')\n", toChars());
        }
        if (members)
        {
            assert(sc);
            sc = sc.push(argsym);
            sc = sc.push(this);
            for (size_t i = 0; i < members.dim; i++)
            {
                Dsymbol s = (*members)[i];
                static if (LOG)
                {
                    printf("\tmember '%s', kind = '%s'\n", s.toChars(), s.kind());
                }
                s.semantic2(sc);
            }
            sc = sc.pop();
            sc.pop();
        }
        static if (LOG)
        {
            printf("-TemplateMixin.semantic2('%s')\n", toChars());
        }
    }

    override void semantic3(Scope* sc)
    {
        if (semanticRun >= PASSsemantic3)
            return;
        semanticRun = PASSsemantic3;
        static if (LOG)
        {
            printf("TemplateMixin.semantic3('%s')\n", toChars());
        }
        if (members)
        {
            sc = sc.push(argsym);
            sc = sc.push(this);
            for (size_t i = 0; i < members.dim; i++)
            {
                Dsymbol s = (*members)[i];
                s.semantic3(sc);
            }
            sc = sc.pop();
            sc.pop();
        }
    }

    override const(char)* kind() const
    {
        return "mixin";
    }

    override bool oneMember(Dsymbol* ps, Identifier ident)
    {
        return Dsymbol.oneMember(ps, ident);
    }

    override int apply(Dsymbol_apply_ft_t fp, void* param)
    {
        if (_scope) // if fwd reference
            semantic(null); // try to resolve it
        if (members)
        {
            for (size_t i = 0; i < members.dim; i++)
            {
                Dsymbol s = (*members)[i];
                if (s)
                {
                    if (s.apply(fp, param))
                        return 1;
                }
            }
        }
        return 0;
    }

    override bool hasPointers()
    {
        //printf("TemplateMixin.hasPointers() %s\n", toChars());
        if (members)
        {
            for (size_t i = 0; i < members.dim; i++)
            {
                Dsymbol s = (*members)[i];
                //printf(" s = %s %s\n", s.kind(), s.toChars());
                if (s.hasPointers())
                {
                    return true;
                }
            }
        }
        return false;
    }

    override void setFieldOffset(AggregateDeclaration ad, uint* poffset, bool isunion)
    {
        //printf("TemplateMixin.setFieldOffset() %s\n", toChars());
        if (_scope) // if fwd reference
            semantic(null); // try to resolve it
        if (members)
        {
            for (size_t i = 0; i < members.dim; i++)
            {
                Dsymbol s = (*members)[i];
                //printf("\t%s\n", s.toChars());
                s.setFieldOffset(ad, poffset, isunion);
            }
        }
    }

    override const(char)* toChars()
    {
        OutBuffer buf;
        toCBufferInstance(this, &buf);
        return buf.extractString();
    }

    bool findTempDecl(Scope* sc)
    {
        // Follow qualifications to find the TemplateDeclaration
        if (!tempdecl)
        {
            Expression e;
            Type t;
            Dsymbol s;
            tqual.resolve(loc, sc, &e, &t, &s);
            if (!s)
            {
                error("is not defined");
                return false;
            }
            s = s.toAlias();
            tempdecl = s.isTemplateDeclaration();
            OverloadSet os = s.isOverloadSet();

            /* If an OverloadSet, look for a unique member that is a template declaration
             */
            if (os)
            {
                Dsymbol ds = null;
                for (size_t i = 0; i < os.a.dim; i++)
                {
                    Dsymbol s2 = os.a[i].isTemplateDeclaration();
                    if (s2)
                    {
                        if (ds)
                        {
                            tempdecl = os;
                            break;
                        }
                        ds = s2;
                    }
                }
            }
            if (!tempdecl)
            {
                error("%s isn't a template", s.toChars());
                return false;
            }
        }
        assert(tempdecl);

        // Look for forward references
        auto tovers = tempdecl.isOverloadSet();
        foreach (size_t oi; 0 .. tovers ? tovers.a.dim : 1)
        {
            Dsymbol dstart = tovers ? tovers.a[oi] : tempdecl;
            int r = overloadApply(dstart, (Dsymbol s)
            {
                auto td = s.isTemplateDeclaration();
                if (!td)
                    return 0;

                if (td.semanticRun == PASSinit)
                {
                    if (td._scope)
                        td.semantic(td._scope);
                    else
                    {
                        semanticRun = PASSinit;
                        return 1;
                    }
                }
                return 0;
            });
            if (r)
                return false;
        }
        return true;
    }

    override inout(TemplateMixin) isTemplateMixin() inout
    {
        return this;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/************************************
 * This struct is needed for TemplateInstance to be the key in an associative array.
 * Fixing https://issues.dlang.org/show_bug.cgi?id=15812 and
 * https://issues.dlang.org/show_bug.cgi?id=15813 would make it unnecessary.
 */
struct TemplateInstanceBox
{
    TemplateInstance ti;

    this(TemplateInstance ti)
    {
        this.ti = ti;
        this.ti.toHash();
        assert(this.ti.hash);
    }

    size_t toHash() const @trusted pure nothrow
    {
        assert(ti.hash);
        return ti.hash;
    }

    bool opEquals(ref const TemplateInstanceBox s) @trusted const
    {
        bool res = void;
        if (ti.inst && s.ti.inst)
            /* This clause is only used when an instance with errors
             * is replaced with a correct instance.
             */
            res = ti is s.ti;
        else
            /* Used when a proposed instance is used to see if there's
             * an existing instance.
             */
            res = (cast()s.ti).compare(cast()ti) == 0;

        debug (FindExistingInstance) ++(res ? nHits : nCollisions);
        return res;
    }

    debug (FindExistingInstance)
    {
        __gshared uint nHits, nCollisions;

        shared static ~this()
        {
            printf("debug (FindExistingInstance) TemplateInstanceBox.equals hits: %u collisions: %u\n",
                   nHits, nCollisions);
        }
    }
}
