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 // The original source code is from: 6 // https://code.google.com/p/libphonenumber/source/browse/trunk/cpp/src/phonenumbers/base/template_util.h?r=621 7 8 #ifndef I18N_ADDRESSINPUT_UTIL_TEMPLATE_UTIL_H_ 9 #define I18N_ADDRESSINPUT_UTIL_TEMPLATE_UTIL_H_ 10 11 #include <cstddef> // For size_t. 12 13 namespace i18n { 14 namespace addressinput { 15 16 // template definitions from tr1 17 18 template<class T, T v> 19 struct integral_constant { 20 static const T value = v; 21 typedef T value_type; 22 typedef integral_constant<T, v> type; 23 }; 24 25 template <class T, T v> const T integral_constant<T, v>::value; 26 27 typedef integral_constant<bool, true> true_type; 28 typedef integral_constant<bool, false> false_type; 29 30 template <class T> struct is_pointer : false_type {}; 31 template <class T> struct is_pointer<T*> : true_type {}; 32 33 template <class T, class U> struct is_same : public false_type {}; 34 template <class T> struct is_same<T,T> : true_type {}; 35 36 template<class> struct is_array : public false_type {}; 37 template<class T, size_t n> struct is_array<T[n]> : public true_type {}; 38 template<class T> struct is_array<T[]> : public true_type {}; 39 40 template <class T> struct is_non_const_reference : false_type {}; 41 template <class T> struct is_non_const_reference<T&> : true_type {}; 42 template <class T> struct is_non_const_reference<const T&> : false_type {}; 43 44 template <class T> struct is_void : false_type {}; 45 template <> struct is_void<void> : true_type {}; 46 47 namespace internal { 48 49 // Types YesType and NoType are guaranteed such that sizeof(YesType) < 50 // sizeof(NoType). 51 typedef char YesType; 52 53 struct NoType { 54 YesType dummy[2]; 55 }; 56 57 // This class is an implementation detail for is_convertible, and you 58 // don't need to know how it works to use is_convertible. For those 59 // who care: we declare two different functions, one whose argument is 60 // of type To and one with a variadic argument list. We give them 61 // return types of different size, so we can use sizeof to trick the 62 // compiler into telling us which function it would have chosen if we 63 // had called it with an argument of type From. See Alexandrescu's 64 // _Modern C++ Design_ for more details on this sort of trick. 65 66 struct ConvertHelper { 67 template <typename To> 68 static YesType Test(To); 69 70 template <typename To> 71 static NoType Test(...); 72 73 template <typename From> 74 static From& Create(); 75 }; 76 77 // Used to determine if a type is a struct/union/class. Inspired by Boost's 78 // is_class type_trait implementation. 79 struct IsClassHelper { 80 template <typename C> 81 static YesType Test(void(C::*)(void)); 82 83 template <typename C> 84 static NoType Test(...); 85 }; 86 87 } // namespace internal 88 89 // Inherits from true_type if From is convertible to To, false_type otherwise. 90 // 91 // Note that if the type is convertible, this will be a true_type REGARDLESS 92 // of whether or not the conversion would emit a warning. 93 template <typename From, typename To> 94 struct is_convertible 95 : integral_constant<bool, 96 sizeof(internal::ConvertHelper::Test<To>( 97 internal::ConvertHelper::Create<From>())) == 98 sizeof(internal::YesType)> { 99 }; 100 101 template <typename T> 102 struct is_class 103 : integral_constant<bool, 104 sizeof(internal::IsClassHelper::Test<T>(0)) == 105 sizeof(internal::YesType)> { 106 }; 107 108 } // namespace addressinput 109 } // namespace i18n 110 111 #endif // I18N_ADDRESSINPUT_UTIL_TEMPLATE_UTIL_H_ 112
