1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_TEMPLATE_UTIL_H_ 6 #define BASE_TEMPLATE_UTIL_H_ 7 8 #include <cstddef> // For size_t. 9 10 #include "build/build_config.h" 11 12 namespace base { 13 14 // template definitions from tr1 15 16 template<class T, T v> 17 struct integral_constant { 18 static const T value = v; 19 typedef T value_type; 20 typedef integral_constant<T, v> type; 21 }; 22 23 template <class T, T v> const T integral_constant<T, v>::value; 24 25 typedef integral_constant<bool, true> true_type; 26 typedef integral_constant<bool, false> false_type; 27 28 template <class T> struct is_pointer : false_type {}; 29 template <class T> struct is_pointer<T*> : true_type {}; 30 31 // Member function pointer detection up to four params. Add more as needed 32 // below. This is built-in to C++ 11, and we can remove this when we switch. 33 template<typename T> 34 struct is_member_function_pointer : false_type {}; 35 36 template <typename R, typename Z> 37 struct is_member_function_pointer<R(Z::*)()> : true_type {}; 38 template <typename R, typename Z> 39 struct is_member_function_pointer<R(Z::*)() const> : true_type {}; 40 41 template <typename R, typename Z, typename A> 42 struct is_member_function_pointer<R(Z::*)(A)> : true_type {}; 43 template <typename R, typename Z, typename A> 44 struct is_member_function_pointer<R(Z::*)(A) const> : true_type {}; 45 46 template <typename R, typename Z, typename A, typename B> 47 struct is_member_function_pointer<R(Z::*)(A, B)> : true_type {}; 48 template <typename R, typename Z, typename A, typename B> 49 struct is_member_function_pointer<R(Z::*)(A, B) const> : true_type {}; 50 51 template <typename R, typename Z, typename A, typename B, typename C> 52 struct is_member_function_pointer<R(Z::*)(A, B, C)> : true_type {}; 53 template <typename R, typename Z, typename A, typename B, typename C> 54 struct is_member_function_pointer<R(Z::*)(A, B, C) const> : true_type {}; 55 56 template <typename R, typename Z, typename A, typename B, typename C, 57 typename D> 58 struct is_member_function_pointer<R(Z::*)(A, B, C, D)> : true_type {}; 59 template <typename R, typename Z, typename A, typename B, typename C, 60 typename D> 61 struct is_member_function_pointer<R(Z::*)(A, B, C, D) const> : true_type {}; 62 63 64 template <class T, class U> struct is_same : public false_type {}; 65 template <class T> struct is_same<T,T> : true_type {}; 66 67 template<class> struct is_array : public false_type {}; 68 template<class T, size_t n> struct is_array<T[n]> : public true_type {}; 69 template<class T> struct is_array<T[]> : public true_type {}; 70 71 template <class T> struct is_non_const_reference : false_type {}; 72 template <class T> struct is_non_const_reference<T&> : true_type {}; 73 template <class T> struct is_non_const_reference<const T&> : false_type {}; 74 75 template <class T> struct is_const : false_type {}; 76 template <class T> struct is_const<const T> : true_type {}; 77 78 template <class T> struct is_void : false_type {}; 79 template <> struct is_void<void> : true_type {}; 80 81 namespace internal { 82 83 // Types YesType and NoType are guaranteed such that sizeof(YesType) < 84 // sizeof(NoType). 85 typedef char YesType; 86 87 struct NoType { 88 YesType dummy[2]; 89 }; 90 91 // This class is an implementation detail for is_convertible, and you 92 // don't need to know how it works to use is_convertible. For those 93 // who care: we declare two different functions, one whose argument is 94 // of type To and one with a variadic argument list. We give them 95 // return types of different size, so we can use sizeof to trick the 96 // compiler into telling us which function it would have chosen if we 97 // had called it with an argument of type From. See Alexandrescu's 98 // _Modern C++ Design_ for more details on this sort of trick. 99 100 struct ConvertHelper { 101 template <typename To> 102 static YesType Test(To); 103 104 template <typename To> 105 static NoType Test(...); 106 107 template <typename From> 108 static From& Create(); 109 }; 110 111 // Used to determine if a type is a struct/union/class. Inspired by Boost's 112 // is_class type_trait implementation. 113 struct IsClassHelper { 114 template <typename C> 115 static YesType Test(void(C::*)(void)); 116 117 template <typename C> 118 static NoType Test(...); 119 }; 120 121 } // namespace internal 122 123 // Inherits from true_type if From is convertible to To, false_type otherwise. 124 // 125 // Note that if the type is convertible, this will be a true_type REGARDLESS 126 // of whether or not the conversion would emit a warning. 127 template <typename From, typename To> 128 struct is_convertible 129 : integral_constant<bool, 130 sizeof(internal::ConvertHelper::Test<To>( 131 internal::ConvertHelper::Create<From>())) == 132 sizeof(internal::YesType)> { 133 }; 134 135 template <typename T> 136 struct is_class 137 : integral_constant<bool, 138 sizeof(internal::IsClassHelper::Test<T>(0)) == 139 sizeof(internal::YesType)> { 140 }; 141 142 template<bool B, class T = void> 143 struct enable_if {}; 144 145 template<class T> 146 struct enable_if<true, T> { typedef T type; }; 147 148 } // namespace base 149 150 #endif // BASE_TEMPLATE_UTIL_H_ 151