1 // Copyright (c) 2010 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 #pragma once 8 9 #include <cstddef> // For size_t. 10 11 #include "build/build_config.h" 12 13 namespace base { 14 15 // template definitions from tr1 16 17 template<class T, T v> 18 struct integral_constant { 19 static const T value = v; 20 typedef T value_type; 21 typedef integral_constant<T, v> type; 22 }; 23 24 template <class T, T v> const T integral_constant<T, v>::value; 25 26 typedef integral_constant<bool, true> true_type; 27 typedef integral_constant<bool, false> false_type; 28 29 template <class T> struct is_pointer : false_type {}; 30 template <class T> struct is_pointer<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 namespace internal { 41 42 // Types YesType and NoType are guaranteed such that sizeof(YesType) < 43 // sizeof(NoType). 44 typedef char YesType; 45 46 struct NoType { 47 YesType dummy[2]; 48 }; 49 50 // This class is an implementation detail for is_convertible, and you 51 // don't need to know how it works to use is_convertible. For those 52 // who care: we declare two different functions, one whose argument is 53 // of type To and one with a variadic argument list. We give them 54 // return types of different size, so we can use sizeof to trick the 55 // compiler into telling us which function it would have chosen if we 56 // had called it with an argument of type From. See Alexandrescu's 57 // _Modern C++ Design_ for more details on this sort of trick. 58 59 struct ConvertHelper { 60 template <typename To> 61 static YesType Test(To); 62 63 template <typename To> 64 static NoType Test(...); 65 66 template <typename From> 67 static From Create(); 68 }; 69 70 // Used to determine if a type is a struct/union/class. Inspired by Boost's 71 // is_class type_trait implementation. 72 struct IsClassHelper { 73 template <typename C> 74 static YesType Test(void(C::*)(void)); 75 76 template <typename C> 77 static NoType Test(...); 78 }; 79 80 } // namespace internal 81 82 // Inherits from true_type if From is convertible to To, false_type otherwise. 83 // 84 // Note that if the type is convertible, this will be a true_type REGARDLESS 85 // of whether or not the conversion would emit a warning. 86 template <typename From, typename To> 87 struct is_convertible 88 : integral_constant<bool, 89 sizeof(internal::ConvertHelper::Test<To>( 90 internal::ConvertHelper::Create<From>())) == 91 sizeof(internal::YesType)> { 92 }; 93 94 template <typename T> 95 struct is_class 96 : integral_constant<bool, 97 sizeof(internal::IsClassHelper::Test<T>(0)) == 98 sizeof(internal::YesType)> { 99 }; 100 101 } // namespace base 102 103 #endif // BASE_TEMPLATE_UTIL_H_ 104
