mfbt/TypeTraits.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* Template-based metaprogramming and type-testing facilities. */
   8
   9 #ifndef mozilla_TypeTraits_h
  10 #define mozilla_TypeTraits_h
  11
  12 #include "mozilla/Types.h"
  13
  14 #include <type_traits>
  15 #include <utility>
  16
  17 /*
  18  * These traits are approximate copies of the traits and semantics from C++11's
  19  * <type_traits> header.  Don't add traits not in that header!  When all
  20  * platforms provide that header, we can convert all users and remove this one.
  21  */
  22
  23 namespace mozilla {
  24
  25 /* 20.9.4 Unary type traits [meta.unary] */
  26
  27 /* 20.9.4.3 Type properties [meta.unary.prop] */
  28
  29 /**
  30  * Traits class for identifying POD types.  Until C++11 there's no automatic
  31  * way to detect PODs, so for the moment this is done manually.  Users may
  32  * define specializations of this class that inherit from std::true_type and
  33  * std::false_type (or equivalently std::integral_constant<bool, true or
  34  * false>, or conveniently from mozilla::IsPod for composite types) as needed to
  35  * ensure correct IsPod behavior.
  36  */
  37 template <typename T>
  38 struct IsPod : public std::false_type {};
  39
  40 template <>
  41 struct IsPod<char> : std::true_type {};
  42 template <>
  43 struct IsPod<signed char> : std::true_type {};
  44 template <>
  45 struct IsPod<unsigned char> : std::true_type {};
  46 template <>
  47 struct IsPod<short> : std::true_type {};
  48 template <>
  49 struct IsPod<unsigned short> : std::true_type {};
  50 template <>
  51 struct IsPod<int> : std::true_type {};
  52 template <>
  53 struct IsPod<unsigned int> : std::true_type {};
  54 template <>
  55 struct IsPod<long> : std::true_type {};
  56 template <>
  57 struct IsPod<unsigned long> : std::true_type {};
  58 template <>
  59 struct IsPod<long long> : std::true_type {};
  60 template <>
  61 struct IsPod<unsigned long long> : std::true_type {};
  62 template <>
  63 struct IsPod<bool> : std::true_type {};
  64 template <>
  65 struct IsPod<float> : std::true_type {};
  66 template <>
  67 struct IsPod<double> : std::true_type {};
  68 template <>
  69 struct IsPod<wchar_t> : std::true_type {};
  70 template <>
  71 struct IsPod<char16_t> : std::true_type {};
  72 template <typename T>
  73 struct IsPod<T*> : std::true_type {};
  74
  75 namespace detail {
  76
  77 struct DoIsDestructibleImpl {
  78   template <typename T, typename = decltype(std::declval<T&>().~T())>
  79   static std::true_type test(int);
  80   template <typename T>
  81   static std::false_type test(...);
  82 };
  83
  84 template <typename T>
  85 struct IsDestructibleImpl : public DoIsDestructibleImpl {
  86   typedef decltype(test<T>(0)) Type;
  87 };
  88
  89 }  // namespace detail
  90
  91 /**
  92  * IsDestructible determines whether a type has a public destructor.
  93  *
  94  * struct S0 {};                    // Implicit default destructor.
  95  * struct S1 { ~S1(); };
  96  * class C2 { ~C2(); };             // private destructor.
  97  *
  98  * mozilla::IsDestructible<S0>::value is true;
  99  * mozilla::IsDestructible<S1>::value is true;
 100  * mozilla::IsDestructible<C2>::value is false.
 101  */
 102 template <typename T>
 103 struct IsDestructible : public detail::IsDestructibleImpl<T>::Type {};
 104
 105 } /* namespace mozilla */
 106
 107 #endif /* mozilla_TypeTraits_h */