1 #ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED 2 #define BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED 3 4 // 5 // Copyright 2015 Peter Dimov 6 // 7 // Distributed under the Boost Software License, Version 1.0. 8 // See accompanying file LICENSE_1_0.txt or copy at 9 // http://www.boost.org/LICENSE_1_0.txt 10 // 11 12 #include <boost/config.hpp> 13 #include <boost/type_traits/decay.hpp> 14 #include <boost/type_traits/declval.hpp> 15 #include <boost/detail/workaround.hpp> 16 17 #if defined(BOOST_NO_CXX11_DECLTYPE) 18 #include <boost/type_traits/detail/common_type_impl.hpp> 19 #endif 20 21 #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 22 #include <boost/type_traits/detail/mp_defer.hpp> 23 #endif 24 25 namespace boost 26 { 27 28 // variadic common_type 29 30 #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 31 32 template<class... T> struct common_type 33 { 34 }; 35 36 #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) 37 38 template<class... T> using common_type_t = typename common_type<T...>::type; 39 40 namespace type_traits_detail 41 { 42 43 template<class T1, class T2, class... T> using common_type_fold = common_type_t<common_type_t<T1, T2>, T...>; 44 45 } // namespace type_traits_detail 46 47 template<class T1, class T2, class... T> 48 struct common_type<T1, T2, T...>: type_traits_detail::mp_defer<type_traits_detail::common_type_fold, T1, T2, T...> 49 { 50 }; 51 52 #else 53 54 template<class T1, class T2, class... T> 55 struct common_type<T1, T2, T...>: common_type<typename common_type<T1, T2>::type, T...> 56 { 57 }; 58 59 #endif // !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) 60 61 #else 62 63 template< 64 class T1 = void, class T2 = void, class T3 = void, 65 class T4 = void, class T5 = void, class T6 = void, 66 class T7 = void, class T8 = void, class T9 = void 67 > 68 struct common_type: common_type<typename common_type<T1, T2>::type, T3, T4, T5, T6, T7, T8, T9> 69 { 70 }; 71 72 #endif // !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 73 74 // one argument 75 76 template<class T> struct common_type<T>: boost::decay<T> 77 { 78 }; 79 80 // two arguments 81 82 namespace type_traits_detail 83 { 84 85 // binary common_type 86 87 #if !defined(BOOST_NO_CXX11_DECLTYPE) 88 89 #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 90 91 #if !defined(BOOST_MSVC) || BOOST_MSVC > 1800 92 93 // internal compiler error on msvc-12.0 94 95 template<class T1, class T2> using builtin_common_type = typename boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )>::type; 96 97 template<class T1, class T2> struct common_type_impl: mp_defer<builtin_common_type, T1, T2> 98 { 99 }; 100 101 #else 102 103 template<class T1, class T2> using builtin_common_type = decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() ); 104 105 template<class T1, class T2> struct common_type_impl_2: mp_defer<builtin_common_type, T1, T2> 106 { 107 }; 108 109 template<class T1, class T2> using decay_common_type = typename boost::decay<typename common_type_impl_2<T1, T2>::type>::type; 110 111 template<class T1, class T2> struct common_type_impl: mp_defer<decay_common_type, T1, T2> 112 { 113 }; 114 115 #endif // !defined(BOOST_MSVC) || BOOST_MSVC > 1800 116 117 #else 118 119 template<class T1, class T2> struct common_type_impl: boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )> 120 { 121 }; 122 123 #endif // #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 124 125 #endif // #if !defined(BOOST_NO_CXX11_DECLTYPE) 126 127 // decay helper 128 129 template<class T1, class T2, class T1d = typename boost::decay<T1>::type, class T2d = typename boost::decay<T2>::type> struct common_type_decay_helper: boost::common_type<T1d, T2d> 130 { 131 }; 132 133 template<class T1, class T2> struct common_type_decay_helper<T1, T2, T1, T2>: common_type_impl<T1, T2> 134 { 135 }; 136 137 } // type_traits_detail 138 139 template<class T1, class T2> struct common_type<T1, T2>: type_traits_detail::common_type_decay_helper<T1, T2> 140 { 141 }; 142 143 } // namespace boost 144 145 #endif // #ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED 146