template_util.h revision 5821806d5e7f356e8fa4b058a389a808ea183019
15821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Copyright (c) 2011 The Chromium Authors. All rights reserved. 25821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Use of this source code is governed by a BSD-style license that can be 35821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// found in the LICENSE file. 45821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 55821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#ifndef BASE_TEMPLATE_UTIL_H_ 65821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#define BASE_TEMPLATE_UTIL_H_ 75821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 85821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include <cstddef> // For size_t. 95821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "build/build_config.h" 115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace base { 135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// template definitions from tr1 155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<class T, T v> 175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct integral_constant { 185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static const T value = v; 195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) typedef T value_type; 205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) typedef integral_constant<T, v> type; 215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T, T v> const T integral_constant<T, v>::value; 245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)typedef integral_constant<bool, true> true_type; 265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)typedef integral_constant<bool, false> false_type; 275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> struct is_pointer : false_type {}; 295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> struct is_pointer<T*> : true_type {}; 305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T, class U> struct is_same : public false_type {}; 325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> struct is_same<T,T> : true_type {}; 335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<class> struct is_array : public false_type {}; 355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<class T, size_t n> struct is_array<T[n]> : public true_type {}; 365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template<class T> struct is_array<T[]> : public true_type {}; 375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> struct is_non_const_reference : false_type {}; 395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> struct is_non_const_reference<T&> : true_type {}; 405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> struct is_non_const_reference<const T&> : false_type {}; 415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <class T> struct is_void : false_type {}; 435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <> struct is_void<void> : true_type {}; 445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace internal { 465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Types YesType and NoType are guaranteed such that sizeof(YesType) < 485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// sizeof(NoType). 495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)typedef char YesType; 505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct NoType { 525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) YesType dummy[2]; 535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// This class is an implementation detail for is_convertible, and you 565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// don't need to know how it works to use is_convertible. For those 575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// who care: we declare two different functions, one whose argument is 585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// of type To and one with a variadic argument list. We give them 595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// return types of different size, so we can use sizeof to trick the 605821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// compiler into telling us which function it would have chosen if we 615821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// had called it with an argument of type From. See Alexandrescu's 625821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// _Modern C++ Design_ for more details on this sort of trick. 635821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 645821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct ConvertHelper { 655821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template <typename To> 665821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static YesType Test(To); 675821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 685821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template <typename To> 695821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static NoType Test(...); 705821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 715821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template <typename From> 725821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static From& Create(); 735821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 745821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 755821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Used to determine if a type is a struct/union/class. Inspired by Boost's 765821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// is_class type_trait implementation. 775821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct IsClassHelper { 785821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template <typename C> 795821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static YesType Test(void(C::*)(void)); 805821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 815821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) template <typename C> 825821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static NoType Test(...); 835821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 845821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 855821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace internal 865821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 875821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Inherits from true_type if From is convertible to To, false_type otherwise. 885821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 895821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Note that if the type is convertible, this will be a true_type REGARDLESS 905821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// of whether or not the conversion would emit a warning. 915821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename From, typename To> 925821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct is_convertible 935821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) : integral_constant<bool, 945821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) sizeof(internal::ConvertHelper::Test<To>( 955821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) internal::ConvertHelper::Create<From>())) == 965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) sizeof(internal::YesType)> { 975821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 985821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 995821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)template <typename T> 1005821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct is_class 1015821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) : integral_constant<bool, 1025821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) sizeof(internal::IsClassHelper::Test<T>(0)) == 1035821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) sizeof(internal::YesType)> { 1045821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1055821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1065821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace base 1075821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1085821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#endif // BASE_TEMPLATE_UTIL_H_ 109