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Last update Sun Jun 13 09:38:39 2010

# std.traits

Templates with which to extract information about types and symbols at compile time.

License:
Boost License 1.0.

Authors:
Walter Bright, Tomasz Stachowiak (isExpressionTuple), Andrei Alexandrescu, Shin Fujishiro

Copyright Digital Mars 2005 - 2009. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at ) http:
//www.boost.org/LICENSE_1_0.txt

template ReturnType(dg...) if (dg.length == 1 && isCallable!(dg))
  Get the type of the return value from a function, a pointer to function, a delegate, a struct with an opCall, a pointer to a struct with an opCall, or a class with an opCall.

  Example:

       import std.traits;
       int foo();
       ReturnType!(foo) x;   // x is declared as int

template ParameterTypeTuple(dg...) if (dg.length == 1 && isCallable!(dg))
  Get, as a tuple, the types of the parameters to a function, a pointer to function, a delegate, a struct with an opCall, a pointer to a struct with an opCall, or a class with an opCall.

  Example:

      import std.traits;
      int foo(int, long);
      void bar(ParameterTypeTuple!(foo));      // declares void bar(int, long);
      void abc(ParameterTypeTuple!(foo)[1]);   // declares void abc(long);

enum ParameterStorageClass;
template ParameterStorageClassTuple(func...) if (func.length == 1 && isCallable!(func))
  Returns a tuple consisting of the storage classes of the parameters of a function func.

  Example:

      alias ParameterStorageClass STC; // shorten the enum name

      void func(ref int ctx, out real result, real param)
      {
      }
      alias ParameterStorageClassTuple!(func) pstc;
      static assert(pstc.length == 3); // three parameters
      static assert(pstc[0] == STC.REF);
      static assert(pstc[1] == STC.OUT);
      static assert(pstc[2] == STC.NONE);

  NONE
  SCOPE
  OUT
  REF
  LAZY
    These flags can be bitwise OR-ed together to represent complex storage class.

enum FunctionAttribute;
template functionAttributes(func...) if (func.length == 1 && isCallable!(func))
  Returns the attributes attached to a function func.

  Example:

      alias FunctionAttribute FA; // shorten the enum name

      real func(real x) pure nothrow @safe
      {
          return x;
      }
      static assert(functionAttributes!(func) & FA.PURE);
      static assert(functionAttributes!(func) & FA.SAFE);
      static assert(!(functionAttributes!(func) & FA.TRUSTED)); // not @trusted

  NONE
  PURE
  NOTHROW
  REF
  PROPERTY
  TRUSTED
  SAFE
    These flags can be bitwise OR-ed together to represent complex attribute.

template functionLinkage(func...) if (func.length == 1 && isCallable!(func))
  Returns the calling convention of function as a string.

  Example:

      string a = functionLinkage!(writeln!(string, int));
      assert(a == "D"); // extern(D)

      auto fp = &printf;
      string b = functionLinkage!(fp);
      assert(b == "C"); // extern(C)

enum Variadic;
template variadicFunctionStyle(func...) if (func.length == 1 && isCallable!(func))
  Determines what kind of variadic parameters function has.

  Example:

      void func() {}
      static assert(variadicFunctionStyle!(func) == Variadic.NO);

      extern(C) int printf(in char*, ...);
      static assert(variadicFunctionStyle!(printf) == Variadic.C);

  NO
    Function is not variadic.

  C
    Function is a C-style variadic function.

  D
    Function is a D-style variadic function, which uses _argptr and _arguments.

  TYPESAFE
    Function is a typesafe variadic function.

template FunctionTypeOf(func...) if (func.length == 1 && isCallable!(func))
  Get the function type from a callable object func.

  Using builtin typeof on a property function yields the types of the property value, not of the property function itself. Still, FunctionTypeOf is able to obtain function types of properties.

      class C {
          int value() @property;
      }
      static assert(is( typeof(C.value) == int ));
      static assert(is( FunctionTypeOf!(C.value) == function ));

  Note:
  Do not confuse function types with function pointer types; function types are usually used for compile-time reflection purposes.

template FieldTypeTuple(S)
  Get the types of the fields of a struct or class. This consists of the fields that take up memory space, excluding the hidden fields like the virtual function table pointer.

template RepresentationTypeTuple(T...)
  Get the primitive types of the fields of a struct or class, in topological order.

  Example:

      struct S1 { int a; float b; }
      struct S2 { char[] a; union { S1 b; S1 * c; } }
      alias RepresentationTypeTuple!(S2) R;
      assert(R.length == 4
          && is(R[0] == char[]) && is(R[1] == int)
          && is(R[2] == float) && is(R[3] == S1*));

template hasAliasing(T...)
  Returns true if and only if T's representation includes at least one of the following:
  1. a raw pointer U* and U is not immutable;
  2. an array U[] and U is not immutable;
  3. a reference to a class type C and C is not immutable.

template BaseTypeTuple(A)
  Get a TypeTuple of the base class and base interfaces of this class or interface. BaseTypeTuple!(Object) returns the empty type tuple.

  Example:

       import std.traits, std.typetuple, std.stdio;
       interface I { }
       class A { }
       class B : A, I { }

       void main()
       {
           alias BaseTypeTuple!(B) TL;
           writeln(typeid(TL));        // prints: (A,I)
       }

template BaseClassesTuple(T)
  Get a TypeTuple of all base classes of this class, in decreasing order. Interfaces are not included. BaseClassesTuple!(Object) yields the empty type tuple.

  Example:

       import std.traits, std.typetuple, std.stdio;
       interface I { }
       class A { }
       class B : A, I { }
       class C : B { }

       void main()
       {
           alias BaseClassesTuple!(C) TL;
           writeln(typeid(TL));        // prints: (B,A,Object)
       }

template InterfacesTuple(T)
  Get a TypeTuple of all interfaces directly or indirectly inherited by this class or interface. Interfaces do not repeat if multiply implemented. InterfacesTuple!(Object) yields the empty type tuple.

  Example:

       import std.traits, std.typetuple, std.stdio;
       interface I1 { }
       interface I2 { }
       class A : I1, I2 { }
       class B : A, I1 { }
       class C : B { }

       void main()
       {
           alias InterfacesTuple!(C) TL;
           writeln(typeid(TL));        // prints: (I1, I2)
       }

template TransitiveBaseTypeTuple(T)
  Get a TypeTuple of all base classes of T, in decreasing order, followed by T's interfaces. TransitiveBaseTypeTuple!(Object) yields the empty type tuple.

  Example:

       import std.traits, std.typetuple, std.stdio;
       interface I { }
       class A { }
       class B : A, I { }
       class C : B { }

       void main()
       {
           alias TransitiveBaseTypeTuple!(C) TL;
           writeln(typeid(TL));        // prints: (B,A,Object,I)
       }

template MemberFunctionsTuple(C,string name) if (is(C == class) || is(C == interface))
  Returns a tuple of non-static functions with the name name declared in the class or interface C. Covariant duplicates are shrunk into the most derived one.

  Example:

      interface I { I foo(); }
      class B
      {
          real foo(real v) { return v; }
      }
      class C : B, I
      {
          override C foo() { return this; } // covariant overriding of I.foo()
      }
      alias MemberFunctionsTuple!(C, "foo") foos;
      static assert(foos.length == 2);
      static assert(__traits(isSame, foos[0], C.foo));
      static assert(__traits(isSame, foos[1], B.foo));

template CommonType(T...)
  Get the type that all types can be implicitly converted to. Useful e.g. in figuring out an array type from a bunch of initializing values. Returns void if passed an empty list, or if the types have no common type.

  Example:

      alias CommonType!(int, long, short) X;
      assert(is(X == long));
      alias CommonType!(int, char[], short) Y;
      assert(is(Y == void));

template ImplicitConversionTargets(T)
  Returns a tuple with all possible target types of an implicit conversion of a value of type T.

  Important note:

  The possible targets are computed more conservatively than the D 2.005 compiler does, eliminating all dangerous conversions. For example, ImplicitConversionTargets!(double) does not include float.

template isImplicitlyConvertible(From,To)
  Is From implicitly convertible to To?

template isCovariantWith(F,G) if (is(F == function) && is(G == function))
  Determines whether the function type F is covariant with G, i.e., functions of the type F can override ones of the type G.

  Example:

      interface I { I clone(); }
      interface J { J clone(); }
      class C : I
      {
          override C clone()   // covariant overriding of I.clone()
          {
              return new C;
          }
      }

      // C.clone() can override I.clone(), indeed.
      static assert(isCovariantWith!(typeof(C.clone), typeof(I.clone)));

      // C.clone() can't override J.clone(); the return type C is not implicitly
      // convertible to J.
      static assert(isCovariantWith!(typeof(C.clone), typeof(J.clone)));

template isIntegral(T)
  Detect whether T is a built-in integral type. Types bool, char, wchar, and dchar are not considered integral.

template isFloatingPoint(T)
  Detect whether T is a built-in floating point type.

template isNumeric(T)
  Detect whether T is a built-in numeric type (integral or floating point).

template isUnsigned(T)
  Detect whether T is a built-in unsigned numeric type.

template isSigned(T)
  Detect whether T is a built-in signed numeric type.

template isSomeString(T)
  Detect whether T is one of the built-in string types

template isSomeChar(T)
  Detect whether T is one of the built-in character types

template isAssociativeArray(T)
  Detect whether T is an associative array type

template isStaticArray(T : U[N],U,size_t N)
  Detect whether type T is a static array.

template isDynamicArray(T,U = void)
  Detect whether type T is a dynamic array.

template isArray(T)
  Detect whether type T is an array.

template isPointer(T)
  Detect whether type T is a pointer.

template isExpressionTuple(T...)
  Tells whether the tuple T is an expression tuple.

template isTypeTuple(T...)
  Detect whether tuple T is a type tuple.

template isFunctionPointer(T...) if (T.length == 1)
  Detect whether symbol or type T is a function pointer.

template isSomeFunction(T...) if (T.length == 1)
  Detect whether symbol or type T is a function, a function pointer or a delegate.

template isCallable(T...) if (T.length == 1)
  Detect whether T is a callable object, which can be called with the function call operator (...).

template isAbstractFunction(alias method)
  Exactly the same as the builtin traits: __traits(isAbstractFunction, method).

template Unqual(T)
  Removes all qualifiers, if any, from type T.

  Example:

      static assert(is(Unqual!(int) == int));
      static assert(is(Unqual!(const int) == int));
      static assert(is(Unqual!(immutable int) == int));
      static assert(is(Unqual!(shared int) == int));
      static assert(is(Unqual!(shared(const int)) == int));

template OriginalType(T)
  Strips off all typedefs (including enum ones) from type T.

  Example:

      enum E : int { a }
      typedef E F;
      typedef const F G;
      static assert(is(OriginalType!G == const int));

template Unsigned(T)
  Returns the corresponding unsigned type for T. T must be a numeric integral type, otherwise a compile-time error occurs.

template Signed(T)
  Returns the corresponding signed type for T. T must be a numeric integral type, otherwise a compile-time error occurs.

template mostNegative(T)
  Returns the most negative value of the numeric type T.

template mangledName(sth...) if (sth.length == 1)
  Returns the mangled name of symbol or type sth.

  mangledName is the same as builtin .mangleof property, except that the correct names of property functions are obtained.

      module test;
      import std.traits : mangledName;

      class C {
          int value() @property;
      }
      pragma(msg, C.value.mangleof);      // prints "i"
      pragma(msg, mangledName!(C.value)); // prints "_D4test1C5valueMFNdZi"

template Select(bool condition,T,F)
  Aliases itself to T if the boolean condition is true and to F otherwise.

  Example:

      alias Select!(size_t.sizeof == 4, int, long) Int;

A select(bool cond : true, A, B)(A a, lazy B b);
B select(bool cond : false, A, B)(lazy A a, B b);
  If cond is true, returns a without evaluating b. Otherwise, returns b without evaluating a.

Copyright Digital Mars 2005 - 2009. | Page generated by Ddoc.