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 #include <boost/type_traits/is_complete.hpp> 17 #include <boost/type_traits/is_void.hpp> 18 #include <boost/type_traits/is_array.hpp> 19 #include <boost/static_assert.hpp> 20 21 #if defined(BOOST_NO_CXX11_DECLTYPE) 22 #include <boost/type_traits/detail/common_type_impl.hpp> 23 #endif 24 25 #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 26 #include <boost/type_traits/detail/mp_defer.hpp> 27 #endif 28 29 namespace boost 30 { 31 32 // variadic common_type 33 34 #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 35 36 template<class... T> struct common_type 37 { 38 }; 39 40 #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) 41 42 template<class... T> using common_type_t = typename common_type<T...>::type; 43 44 namespace type_traits_detail 45 { 46 47 template<class T1, class T2, class... T> using common_type_fold = common_type_t<common_type_t<T1, T2>, T...>; 48 49 } // namespace type_traits_detail 50 51 template<class T1, class T2, class... T> 52 struct common_type<T1, T2, T...>: type_traits_detail::mp_defer<type_traits_detail::common_type_fold, T1, T2, T...> 53 { 54 }; 55 56 #else 57 58 template<class T1, class T2, class... T> 59 struct common_type<T1, T2, T...>: common_type<typename common_type<T1, T2>::type, T...> 60 { 61 }; 62 63 #endif // !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) 64 65 #else 66 67 template< 68 class T1 = void, class T2 = void, class T3 = void, 69 class T4 = void, class T5 = void, class T6 = void, 70 class T7 = void, class T8 = void, class T9 = void 71 > 72 struct common_type: common_type<typename common_type<T1, T2>::type, T3, T4, T5, T6, T7, T8, T9> 73 { 74 }; 75 76 #endif // !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 77 78 // one argument 79 80 template<class T> struct common_type<T>: boost::decay<T> 81 { 82 BOOST_STATIC_ASSERT_MSG(::boost::is_complete<T>::value || ::boost::is_void<T>::value || ::boost::is_array<T>::value, "Arguments to common_type must both be complete types"); 83 }; 84 85 // two arguments 86 87 namespace type_traits_detail 88 { 89 90 // binary common_type 91 92 #if !defined(BOOST_NO_CXX11_DECLTYPE) 93 94 #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 95 96 #if !defined(BOOST_MSVC) || BOOST_MSVC > 1800 97 98 // internal compiler error on msvc-12.0 99 100 template<class T1, class T2> using builtin_common_type = typename boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )>::type; 101 102 template<class T1, class T2> struct common_type_impl: mp_defer<builtin_common_type, T1, T2> 103 { 104 }; 105 106 #else 107 108 template<class T1, class T2> using builtin_common_type = decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() ); 109 110 template<class T1, class T2> struct common_type_impl_2: mp_defer<builtin_common_type, T1, T2> 111 { 112 }; 113 114 template<class T1, class T2> using decay_common_type = typename boost::decay<typename common_type_impl_2<T1, T2>::type>::type; 115 116 template<class T1, class T2> struct common_type_impl: mp_defer<decay_common_type, T1, T2> 117 { 118 }; 119 120 #endif // !defined(BOOST_MSVC) || BOOST_MSVC > 1800 121 122 #else 123 124 template<class T1, class T2> struct common_type_impl: boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )> 125 { 126 }; 127 128 #endif // #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) 129 130 #endif // #if !defined(BOOST_NO_CXX11_DECLTYPE) 131 132 // decay helper 133 134 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> 135 { 136 }; 137 138 template<class T1, class T2> struct common_type_decay_helper<T1, T2, T1, T2>: common_type_impl<T1, T2> 139 { 140 }; 141 142 } // type_traits_detail 143 144 template<class T1, class T2> struct common_type<T1, T2>: type_traits_detail::common_type_decay_helper<T1, T2> 145 { 146 BOOST_STATIC_ASSERT_MSG(::boost::is_complete<T1>::value || ::boost::is_void<T1>::value || ::boost::is_array<T1>::value, "Arguments to common_type must both be complete types"); 147 BOOST_STATIC_ASSERT_MSG(::boost::is_complete<T2>::value || ::boost::is_void<T2>::value || ::boost::is_array<T2>::value, "Arguments to common_type must both be complete types"); 148 }; 149 150 } // namespace boost 151 152 #endif // #ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED 153