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 <stddef.h> 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. This is built-in to C++ 11's stdlib, and 32 // we can remove this when we switch to it. 33 template<typename T> 34 struct is_member_function_pointer : false_type {}; 35 36 template <typename R, typename Z, typename... A> 37 struct is_member_function_pointer<R(Z::*)(A...)> : true_type {}; 38 template <typename R, typename Z, typename... A> 39 struct is_member_function_pointer<R(Z::*)(A...) const> : true_type {}; 40 41 42 template <class T, class U> struct is_same : public false_type {}; 43 template <class T> struct is_same<T,T> : true_type {}; 44 45 template<class> struct is_array : public false_type {}; 46 template<class T, size_t n> struct is_array<T[n]> : public true_type {}; 47 template<class T> struct is_array<T[]> : public true_type {}; 48 49 template <class T> struct is_non_const_reference : false_type {}; 50 template <class T> struct is_non_const_reference<T&> : true_type {}; 51 template <class T> struct is_non_const_reference<const T&> : false_type {}; 52 53 template <class T> struct is_const : false_type {}; 54 template <class T> struct is_const<const T> : true_type {}; 55 56 template <class T> struct is_void : false_type {}; 57 template <> struct is_void<void> : true_type {}; 58 59 namespace internal { 60 61 // Types YesType and NoType are guaranteed such that sizeof(YesType) < 62 // sizeof(NoType). 63 typedef char YesType; 64 65 struct NoType { 66 YesType dummy[2]; 67 }; 68 69 // This class is an implementation detail for is_convertible, and you 70 // don't need to know how it works to use is_convertible. For those 71 // who care: we declare two different functions, one whose argument is 72 // of type To and one with a variadic argument list. We give them 73 // return types of different size, so we can use sizeof to trick the 74 // compiler into telling us which function it would have chosen if we 75 // had called it with an argument of type From. See Alexandrescu's 76 // _Modern C++ Design_ for more details on this sort of trick. 77 78 struct ConvertHelper { 79 template <typename To> 80 static YesType Test(To); 81 82 template <typename To> 83 static NoType Test(...); 84 85 template <typename From> 86 static From& Create(); 87 }; 88 89 // Used to determine if a type is a struct/union/class. Inspired by Boost's 90 // is_class type_trait implementation. 91 struct IsClassHelper { 92 template <typename C> 93 static YesType Test(void(C::*)(void)); 94 95 template <typename C> 96 static NoType Test(...); 97 }; 98 99 } // namespace internal 100 101 // Inherits from true_type if From is convertible to To, false_type otherwise. 102 // 103 // Note that if the type is convertible, this will be a true_type REGARDLESS 104 // of whether or not the conversion would emit a warning. 105 template <typename From, typename To> 106 struct is_convertible 107 : integral_constant<bool, 108 sizeof(internal::ConvertHelper::Test<To>( 109 internal::ConvertHelper::Create<From>())) == 110 sizeof(internal::YesType)> { 111 }; 112 113 template <typename T> 114 struct is_class 115 : integral_constant<bool, 116 sizeof(internal::IsClassHelper::Test<T>(0)) == 117 sizeof(internal::YesType)> { 118 }; 119 120 } // namespace base 121 122 #endif // BASE_TEMPLATE_UTIL_H_ 123