1 /* 2 * Copyright 2011 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 #ifndef WEBRTC_BASE_TEMPLATE_UTIL_H_ 12 #define WEBRTC_BASE_TEMPLATE_UTIL_H_ 13 14 #include <stddef.h> // For size_t. 15 16 namespace rtc { 17 18 // template definitions from tr1 19 20 template<class T, T v> 21 struct integral_constant { 22 static const T value = v; 23 typedef T value_type; 24 typedef integral_constant<T, v> type; 25 }; 26 27 template <class T, T v> const T integral_constant<T, v>::value; 28 29 typedef integral_constant<bool, true> true_type; 30 typedef integral_constant<bool, false> false_type; 31 32 template <class T> struct is_pointer : false_type {}; 33 template <class T> struct is_pointer<T*> : true_type {}; 34 35 template <class T, class U> struct is_same : public false_type {}; 36 template <class T> struct is_same<T,T> : true_type {}; 37 38 template<class> struct is_array : public false_type {}; 39 template<class T, size_t n> struct is_array<T[n]> : public true_type {}; 40 template<class T> struct is_array<T[]> : public true_type {}; 41 42 template <class T> struct is_non_const_reference : false_type {}; 43 template <class T> struct is_non_const_reference<T&> : true_type {}; 44 template <class T> struct is_non_const_reference<const T&> : false_type {}; 45 46 template <class T> struct is_void : false_type {}; 47 template <> struct is_void<void> : true_type {}; 48 49 namespace internal { 50 51 // Types YesType and NoType are guaranteed such that sizeof(YesType) < 52 // sizeof(NoType). 53 typedef char YesType; 54 55 struct NoType { 56 YesType dummy[2]; 57 }; 58 59 // This class is an implementation detail for is_convertible, and you 60 // don't need to know how it works to use is_convertible. For those 61 // who care: we declare two different functions, one whose argument is 62 // of type To and one with a variadic argument list. We give them 63 // return types of different size, so we can use sizeof to trick the 64 // compiler into telling us which function it would have chosen if we 65 // had called it with an argument of type From. See Alexandrescu's 66 // _Modern C++ Design_ for more details on this sort of trick. 67 68 struct ConvertHelper { 69 template <typename To> 70 static YesType Test(To); 71 72 template <typename To> 73 static NoType Test(...); 74 75 template <typename From> 76 static From& Create(); 77 }; 78 79 // Used to determine if a type is a struct/union/class. Inspired by Boost's 80 // is_class type_trait implementation. 81 struct IsClassHelper { 82 template <typename C> 83 static YesType Test(void(C::*)(void)); 84 85 template <typename C> 86 static NoType Test(...); 87 }; 88 89 } // namespace internal 90 91 // Inherits from true_type if From is convertible to To, false_type otherwise. 92 // 93 // Note that if the type is convertible, this will be a true_type REGARDLESS 94 // of whether or not the conversion would emit a warning. 95 template <typename From, typename To> 96 struct is_convertible 97 : integral_constant<bool, 98 sizeof(internal::ConvertHelper::Test<To>( 99 internal::ConvertHelper::Create<From>())) == 100 sizeof(internal::YesType)> { 101 }; 102 103 template <typename T> 104 struct is_class 105 : integral_constant<bool, 106 sizeof(internal::IsClassHelper::Test<T>(0)) == 107 sizeof(internal::YesType)> { 108 }; 109 110 } // namespace rtc 111 112 #endif // WEBRTC_BASE_TEMPLATE_UTIL_H_ 113
