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 TALK_BASE_TEMPLATE_UTIL_H_ 6 #define TALK_BASE_TEMPLATE_UTIL_H_ 7 8 #include <stddef.h> // For size_t. 9 10 namespace talk_base { 11 12 // template definitions from tr1 13 14 template<class T, T v> 15 struct integral_constant { 16 static const T value = v; 17 typedef T value_type; 18 typedef integral_constant<T, v> type; 19 }; 20 21 template <class T, T v> const T integral_constant<T, v>::value; 22 23 typedef integral_constant<bool, true> true_type; 24 typedef integral_constant<bool, false> false_type; 25 26 template <class T> struct is_pointer : false_type {}; 27 template <class T> struct is_pointer<T*> : true_type {}; 28 29 template <class T, class U> struct is_same : public false_type {}; 30 template <class T> struct is_same<T,T> : true_type {}; 31 32 template<class> struct is_array : public false_type {}; 33 template<class T, size_t n> struct is_array<T[n]> : public true_type {}; 34 template<class T> struct is_array<T[]> : public true_type {}; 35 36 template <class T> struct is_non_const_reference : false_type {}; 37 template <class T> struct is_non_const_reference<T&> : true_type {}; 38 template <class T> struct is_non_const_reference<const T&> : false_type {}; 39 40 template <class T> struct is_void : false_type {}; 41 template <> struct is_void<void> : true_type {}; 42 43 namespace internal { 44 45 // Types YesType and NoType are guaranteed such that sizeof(YesType) < 46 // sizeof(NoType). 47 typedef char YesType; 48 49 struct NoType { 50 YesType dummy[2]; 51 }; 52 53 // This class is an implementation detail for is_convertible, and you 54 // don't need to know how it works to use is_convertible. For those 55 // who care: we declare two different functions, one whose argument is 56 // of type To and one with a variadic argument list. We give them 57 // return types of different size, so we can use sizeof to trick the 58 // compiler into telling us which function it would have chosen if we 59 // had called it with an argument of type From. See Alexandrescu's 60 // _Modern C++ Design_ for more details on this sort of trick. 61 62 struct ConvertHelper { 63 template <typename To> 64 static YesType Test(To); 65 66 template <typename To> 67 static NoType Test(...); 68 69 template <typename From> 70 static From& Create(); 71 }; 72 73 // Used to determine if a type is a struct/union/class. Inspired by Boost's 74 // is_class type_trait implementation. 75 struct IsClassHelper { 76 template <typename C> 77 static YesType Test(void(C::*)(void)); 78 79 template <typename C> 80 static NoType Test(...); 81 }; 82 83 } // namespace internal 84 85 // Inherits from true_type if From is convertible to To, false_type otherwise. 86 // 87 // Note that if the type is convertible, this will be a true_type REGARDLESS 88 // of whether or not the conversion would emit a warning. 89 template <typename From, typename To> 90 struct is_convertible 91 : integral_constant<bool, 92 sizeof(internal::ConvertHelper::Test<To>( 93 internal::ConvertHelper::Create<From>())) == 94 sizeof(internal::YesType)> { 95 }; 96 97 template <typename T> 98 struct is_class 99 : integral_constant<bool, 100 sizeof(internal::IsClassHelper::Test<T>(0)) == 101 sizeof(internal::YesType)> { 102 }; 103 104 } // namespace talk_base 105 106 #endif // TALK_BASE_TEMPLATE_UTIL_H_ 107
