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 I18N_PHONENUMBERS_BASE_TEMPLATE_UTIL_H_ 6 #define I18N_PHONENUMBERS_BASE_TEMPLATE_UTIL_H_ 7 8 #include <cstddef> // For size_t. 9 10 namespace i18n { 11 namespace phonenumbers { 12 13 // template definitions from tr1 14 15 template<class T, T v> 16 struct integral_constant { 17 static const T value = v; 18 typedef T value_type; 19 typedef integral_constant<T, v> type; 20 }; 21 22 template <class T, T v> const T integral_constant<T, v>::value; 23 24 typedef integral_constant<bool, true> true_type; 25 typedef integral_constant<bool, false> false_type; 26 27 template <class T> struct is_pointer : false_type {}; 28 template <class T> struct is_pointer<T*> : true_type {}; 29 30 template <class T, class U> struct is_same : public false_type {}; 31 template <class T> struct is_same<T,T> : true_type {}; 32 33 template<class> struct is_array : public false_type {}; 34 template<class T, size_t n> struct is_array<T[n]> : public true_type {}; 35 template<class T> struct is_array<T[]> : public true_type {}; 36 37 template <class T> struct is_non_const_reference : false_type {}; 38 template <class T> struct is_non_const_reference<T&> : true_type {}; 39 template <class T> struct is_non_const_reference<const T&> : false_type {}; 40 41 template <class T> struct is_void : false_type {}; 42 template <> struct is_void<void> : true_type {}; 43 44 namespace internal { 45 46 // Types YesType and NoType are guaranteed such that sizeof(YesType) < 47 // sizeof(NoType). 48 typedef char YesType; 49 50 struct NoType { 51 YesType dummy[2]; 52 }; 53 54 // This class is an implementation detail for is_convertible, and you 55 // don't need to know how it works to use is_convertible. For those 56 // who care: we declare two different functions, one whose argument is 57 // of type To and one with a variadic argument list. We give them 58 // return types of different size, so we can use sizeof to trick the 59 // compiler into telling us which function it would have chosen if we 60 // had called it with an argument of type From. See Alexandrescu's 61 // _Modern C++ Design_ for more details on this sort of trick. 62 63 struct ConvertHelper { 64 template <typename To> 65 static YesType Test(To); 66 67 template <typename To> 68 static NoType Test(...); 69 70 template <typename From> 71 static From& Create(); 72 }; 73 74 // Used to determine if a type is a struct/union/class. Inspired by Boost's 75 // is_class type_trait implementation. 76 struct IsClassHelper { 77 template <typename C> 78 static YesType Test(void(C::*)(void)); 79 80 template <typename C> 81 static NoType Test(...); 82 }; 83 84 } // namespace internal 85 86 // Inherits from true_type if From is convertible to To, false_type otherwise. 87 // 88 // Note that if the type is convertible, this will be a true_type REGARDLESS 89 // of whether or not the conversion would emit a warning. 90 template <typename From, typename To> 91 struct is_convertible 92 : integral_constant<bool, 93 sizeof(internal::ConvertHelper::Test<To>( 94 internal::ConvertHelper::Create<From>())) == 95 sizeof(internal::YesType)> { 96 }; 97 98 template <typename T> 99 struct is_class 100 : integral_constant<bool, 101 sizeof(internal::IsClassHelper::Test<T>(0)) == 102 sizeof(internal::YesType)> { 103 }; 104 105 } // namespace phonenumbers 106 } // namespace i18n 107 108 #endif // I18N_PHONENUMBERS_BASE_TEMPLATE_UTIL_H_ 109
