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# dmd.dtemplate

Defines TemplateDeclaration, TemplateInstance and a few utilities
This modules holds the two main template types: TemplateDeclaration, which is the user-provided declaration of a template, and TemplateInstance, which is an instance of a TemplateDeclaration with specific arguments.

Template Parameter Additionally, the classes for template parameters are defined in this module. The base class, TemplateParameter, is inherited by: - TemplateTypeParameter - TemplateThisParameter - TemplateValueParameter - TemplateAliasParameter - TemplateTupleParameter

Templates semantic The start of the template instantiation process looks like this: - A TypeInstance or TypeIdentifier is encountered. TypeInstance have a bang (e.g. Foo!(arg)) while TypeIdentifier don't. - A TemplateInstance is instantiated - Semantic is run on the TemplateInstance (see dmd.dsymbolsem) - The TemplateInstance search for its TemplateDeclaration, runs semantic on the template arguments and deduce the best match among the possible overloads. - The TemplateInstance search for existing instances with the same arguments, and uses it if found. - Otherwise, the rest of semantic is run on the TemplateInstance.

Authors:
Walter Bright
License:
Boost License 1.0

Source dtemplate.d

Documentation https://dlang.org/phobos/dmd_dtemplate.html

Coverage https://codecov.io/gh/dlang/dmd/src/master/src/dmd/dtemplate.d

pure nothrow @nogc inout(Expression) `isExpression`(inout RootObject `o`);
  These functions substitute for dynamic_cast. dynamic_cast does not work on earlier versions of gcc.
pure nothrow @nogc bool `isError`(const RootObject `o`);
  Is this Object an error?
pure nothrow @nogc bool `arrayObjectIsError`(const Objects* `args`);
  Are any of the Objects an error?
pure nothrow @nogc inout(Type) `getType`(inout RootObject `o`);
  Try to get arg as a type.
class `TemplateDeclaration`: dmd.dsymbol.ScopeDsymbol;
  [mixin] template Identifier (parameters) [Constraint] https://dlang.org/spec/template.html https://dlang.org/spec/template-mixin.html
  bool `isTrivialAliasSeq`;
    matches pattern template AliasSeq(T...) { alias AliasSeq = T; }
  bool `isTrivialAlias`;
    matches pattern template Alias(T) { alias Alias = qualifiers(T); }
  int `inuse`;
    for recursive expansion detection
  bool `overloadInsert`(Dsymbol `s`);
    Overload existing TemplateDeclaration 'this' with the new one 's'. Return true if successful; i.e. no conflict.
  const(char)* `toCharsNoConstraints`();
    Similar to toChars, but does not print the template constraints
  bool `evaluateConstraint`(TemplateInstance `ti`, Scope* `sc`, Scope* `paramscope`, Objects* `dedargs`, FuncDeclaration `fd`);
    Check to see if constraint is satisfied.
  const(char)* `getConstraintEvalError`(ref const(char)* `tip`);
    Destructively get the error message from the last constraint evaluation
    Parameters:

    const(char)* `tip` | tip to show after printing all overloads

  Scope* `scopeForTemplateParameters`(TemplateInstance `ti`, Scope* `sc`);
    Create a scope for the parameters of the TemplateInstance `ti` in the parent scope sc from the ScopeDsymbol paramsym.
    If paramsym is null a new ScopeDsymbol is used in place of paramsym.
    Parameters:

    TemplateInstance `ti` | the TemplateInstance whose parameters to generate the scope for.
    Scope* `sc` | the parent scope of ti

    Returns:
    a scope for the parameters of ti
  MATCH `matchWithInstance`(Scope* `sc`, TemplateInstance `ti`, Objects* `dedtypes`, Expressions* `fargs`, int `flag`);
    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 `leastAsSpecialized`(Scope* `sc`, TemplateDeclaration `td2`, Expressions* `fargs`);
    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 `deduceFunctionTemplateMatch`(TemplateInstance `ti`, Scope* `sc`, ref FuncDeclaration `fd`, Type `tthis`, Expressions* `fargs`);
    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
  RootObject `declareParameter`(Scope* `sc`, TemplateParameter `tp`, RootObject `o`);
    Declare template parameter tp with value o, and install it in the scope sc.
  FuncDeclaration `doHeaderInstantiation`(TemplateInstance `ti`, Scope* `sc2`, FuncDeclaration `fd`, Type `tthis`, Expressions* `fargs`);
    Limited function template instantiation for using fd.leastAsSpecialized()
  TemplateInstance `findExistingInstance`(TemplateInstance `tithis`, Expressions* `fargs`);
    Given a new instance tithis of this TemplateDeclaration, see if there already exists an instance. If so, return that existing instance.
  TemplateInstance `addInstance`(TemplateInstance `ti`);
    Add instance ti to TemplateDeclaration's table of instances. Return a handle we can use to later remove it if it fails instantiation.
  void `removeInstance`(TemplateInstance `ti`);
    Remove TemplateInstance from table of instances.

    Input handle returned by addInstance()

  TemplateTupleParameter `isVariadic`();
    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
  const bool `isOverloadable`();
    We can overload templates.
void `functionResolve`(ref MatchAccumulator `m`, Dsymbol `dstart`, Loc `loc`, Scope* `sc`, Objects* `tiargs`, Type `tthis`, Expressions* `fargs`, const(char)** `pMessage` = null);
  Given function arguments, figure out which template function to expand, and return matching result.
  Parameters:

  MatchAccumulator `m` | matching result
  Dsymbol `dstart` | the root of overloaded function templates
  Loc `loc` | instantiation location
  Scope* `sc` | instantiation scope
  Objects* `tiargs` | initial list of template arguments
  Type `tthis` | if !NULL, the 'this' pointer argument
  Expressions* `fargs` | arguments to function
  const(char)** `pMessage` | address to store error message, or null

bool `reliesOnTident`(Type `t`, TemplateParameters* `tparams`, size_t `iStart` = 0);
  Check whether the type t representation relies on one or more the template parameters.
  Parameters:

  Type `t` | Tested type, if null, returns false.
  TemplateParameters* `tparams` | Template parameters.
  size_t `iStart` | Start index of tparams to limit the tested parameters. If it's nonzero, tparams[0..iStart] will be excluded from the test target.

abstract class `TemplateParameter`: dmd.ast_node.ASTNode;
  https://dlang.org/spec/template.html#TemplateParameter
class `TemplateTypeParameter`: dmd.dtemplate.TemplateParameter;
  https://dlang.org/spec/template.html#TemplateTypeParameter

  Syntax ident : specType = defaultType

class `TemplateThisParameter`: dmd.dtemplate.TemplateTypeParameter;
  https://dlang.org/spec/template.html#TemplateThisParameter

  Syntax this ident : specType = defaultType

class `TemplateValueParameter`: dmd.dtemplate.TemplateParameter;
  https://dlang.org/spec/template.html#TemplateValueParameter

  Syntax valType ident : specValue = defaultValue

class `TemplateAliasParameter`: dmd.dtemplate.TemplateParameter;
  https://dlang.org/spec/template.html#TemplateAliasParameter

  Syntax specType ident : specAlias = defaultAlias

class `TemplateTupleParameter`: dmd.dtemplate.TemplateParameter;
  https://dlang.org/spec/template.html#TemplateSequenceParameter

  Syntax ident ...

class `TemplateInstance`: dmd.dsymbol.ScopeDsymbol;
  https://dlang.org/spec/template.html#explicit_tmp_instantiation

  Given foo!(args) => name = foo tiargs = args

  this(ref const Loc `loc`, TemplateDeclaration `td`, Objects* `tiargs`);
    This constructor is only called when we figured out which function template to instantiate.
  final void `printInstantiationTrace`();
    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 Identifier `getIdent`();
    Lazily generate identifier for template instance. This is because 75% of the ident's are never needed.
  final bool `equalsx`(TemplateInstance `ti`);
    Compare proposed template instantiation with existing template instantiation. Note that this is not commutative because of the auto ref check.
    Parameters:

    TemplateInstance `ti` | existing template instantiation

    Returns:
    true for match
  final bool `isDiscardable`();
    Returns:
    true if the instances' innards are discardable.
    The idea of this function is to see if the template instantiation can be 100% replaced with its eponymous member. All other members can be discarded, even in the compiler to free memory (for example, the template could be expanded in a region allocator, deemed trivial, the end result copied back out independently and the entire region freed), and can be elided entirely from the binary.
    The current implementation affects code that generally looks like:

        template foo(args...) {
            some_basic_type_or_string helper() { .... }
            enum foo = helper();
        }

    since it was the easiest starting point of implementation but it can and should be expanded more later.
  final bool `needsCodegen`();
    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 `findTempDecl`(Scope* `sc`, WithScopeSymbol* `pwithsym`);
    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 `updateTempDecl`(Scope* `sc`, Dsymbol `s`);
    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.
  static bool `semanticTiargs`(ref const Loc `loc`, Scope* `sc`, Objects* `tiargs`, int `flags`);
    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.
  final bool `semanticTiargs`(Scope* `sc`);
    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 `needsTypeInference`(Scope* `sc`, int `flag` = 0);
    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 `hasNestedArgs`(Objects* `args`, bool `isstatic`);
    Determines if a TemplateInstance will need a nested generation of the TemplateDeclaration. Sets enclosing property if so, and returns != 0;
  final Dsymbols* `appendToModuleMember`();
    Append 'this' to the specific module members[]
  final void `declareParameters`(Scope* `sc`);
    Declare parameters of template instance, initialize them with the template instance arguments.
  final Identifier `genIdent`(Objects* `args`);
    This instance needs an identifier for name mangling purposes. Create one by taking the template declaration name and adding the type signature for it.
void `unSpeculative`(Scope* `sc`, RootObject `o`);
  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.
bool `definitelyValueParameter`(Expression `e`);
  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).
class `TemplateMixin`: dmd.dtemplate.TemplateInstance;
  https://dlang.org/spec/template-mixin.html

  Syntax mixin MixinTemplateName [TemplateArguments] [Identifier];

struct `TemplateInstanceBox`;
  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.
MATCH `matchArg`(TemplateParameter `tp`, Loc `instLoc`, Scope* `sc`, Objects* `tiargs`, size_t `i`, TemplateParameters* `parameters`, Objects* `dedtypes`, Declaration* `psparam`);
  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]

struct `TemplateStats`;
  Collect and print statistics on template instantiations.
  static void `incInstance`(const TemplateDeclaration `td`);
    Add this instance
  static void `incUnique`(const TemplateDeclaration `td`);
    Add this unique instance

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