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