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 13namespace base { 14 15// template definitions from tr1 16 17template<class T, T v> 18struct integral_constant { 19 static const T value = v; 20 typedef T value_type; 21 typedef integral_constant<T, v> type; 22}; 23 24template <class T, T v> const T integral_constant<T, v>::value; 25 26typedef integral_constant<bool, true> true_type; 27typedef integral_constant<bool, false> false_type; 28 29template <class T> struct is_pointer : false_type {}; 30template <class T> struct is_pointer<T*> : true_type {}; 31 32template<class> struct is_array : public false_type {}; 33template<class T, size_t n> struct is_array<T[n]> : public true_type {}; 34template<class T> struct is_array<T[]> : public true_type {}; 35 36template <class T> struct is_non_const_reference : false_type {}; 37template <class T> struct is_non_const_reference<T&> : true_type {}; 38template <class T> struct is_non_const_reference<const T&> : false_type {}; 39 40namespace internal { 41 42// Types YesType and NoType are guaranteed such that sizeof(YesType) < 43// sizeof(NoType). 44typedef char YesType; 45 46struct 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 59struct 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. 72struct 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. 86template <typename From, typename To> 87struct is_convertible 88 : integral_constant<bool, 89 sizeof(internal::ConvertHelper::Test<To>( 90 internal::ConvertHelper::Create<From>())) == 91 sizeof(internal::YesType)> { 92}; 93 94template <typename T> 95struct 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