1 /* 2 * Copyright (c) 2013 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 // Borrowed from Chromium's src/base/template_util.h. 12 13 #ifndef WEBRTC_BASE_TEMPLATE_UTIL_H_ 14 #define WEBRTC_BASE_TEMPLATE_UTIL_H_ 15 16 #include <stddef.h> // For size_t. 17 18 namespace rtc { 19 20 // Template definitions from tr1. 21 22 template<class T, T v> 23 struct integral_constant { 24 static const T value = v; 25 typedef T value_type; 26 typedef integral_constant<T, v> type; 27 }; 28 29 template <class T, T v> const T integral_constant<T, v>::value; 30 31 typedef integral_constant<bool, true> true_type; 32 typedef integral_constant<bool, false> false_type; 33 34 template <class T> struct is_pointer : false_type {}; 35 template <class T> struct is_pointer<T*> : true_type {}; 36 37 template <class T, class U> struct is_same : public false_type {}; 38 template <class T> struct is_same<T, T> : true_type {}; 39 40 template<class> struct is_array : public false_type {}; 41 template<class T, size_t n> struct is_array<T[n]> : public true_type {}; 42 template<class T> struct is_array<T[]> : public true_type {}; 43 44 template <class T> struct is_non_const_reference : false_type {}; 45 template <class T> struct is_non_const_reference<T&> : true_type {}; 46 template <class T> struct is_non_const_reference<const T&> : false_type {}; 47 48 template <class T> struct is_void : false_type {}; 49 template <> struct is_void<void> : true_type {}; 50 51 template <class T> 52 struct remove_reference { 53 typedef T type; 54 }; 55 template <class T> 56 struct remove_reference<T&> { 57 typedef T type; 58 }; 59 template <class T> 60 struct remove_reference<T&&> { 61 typedef T type; 62 }; 63 64 namespace internal { 65 66 // Types YesType and NoType are guaranteed such that sizeof(YesType) < 67 // sizeof(NoType). 68 typedef char YesType; 69 70 struct NoType { 71 YesType dummy[2]; 72 }; 73 74 // This class is an implementation detail for is_convertible, and you 75 // don't need to know how it works to use is_convertible. For those 76 // who care: we declare two different functions, one whose argument is 77 // of type To and one with a variadic argument list. We give them 78 // return types of different size, so we can use sizeof to trick the 79 // compiler into telling us which function it would have chosen if we 80 // had called it with an argument of type From. See Alexandrescu's 81 // _Modern C++ Design_ for more details on this sort of trick. 82 83 struct ConvertHelper { 84 template <typename To> 85 static YesType Test(To); 86 87 template <typename To> 88 static NoType Test(...); 89 90 template <typename From> 91 static From& Create(); 92 }; 93 94 // Used to determine if a type is a struct/union/class. Inspired by Boost's 95 // is_class type_trait implementation. 96 struct IsClassHelper { 97 template <typename C> 98 static YesType Test(void(C::*)(void)); 99 100 template <typename C> 101 static NoType Test(...); 102 }; 103 104 } // namespace internal 105 106 // Inherits from true_type if From is convertible to To, false_type otherwise. 107 // 108 // Note that if the type is convertible, this will be a true_type REGARDLESS 109 // of whether or not the conversion would emit a warning. 110 template <typename From, typename To> 111 struct is_convertible 112 : integral_constant<bool, 113 sizeof(internal::ConvertHelper::Test<To>( 114 internal::ConvertHelper::Create<From>())) == 115 sizeof(internal::YesType)> { 116 }; 117 118 template <typename T> 119 struct is_class 120 : integral_constant<bool, 121 sizeof(internal::IsClassHelper::Test<T>(0)) == 122 sizeof(internal::YesType)> { 123 }; 124 125 } // namespace rtc 126 127 #endif // WEBRTC_BASE_TEMPLATE_UTIL_H_ 128
