1 #ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED
2 #define BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED
5 // Copyright 2015 Peter Dimov
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
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>
17 #if defined(BOOST_NO_CXX11_DECLTYPE)
18 #include <boost/type_traits/detail/common_type_impl.hpp>
21 #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
22 #include <boost/type_traits/detail/mp_defer.hpp>
28 // variadic common_type
30 #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
32 template<class... T> struct common_type
36 #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES)
38 template<class... T> using common_type_t = typename common_type<T...>::type;
40 namespace type_traits_detail
43 template<class T1, class T2, class... T> using common_type_fold = common_type_t<common_type_t<T1, T2>, T...>;
45 } // namespace type_traits_detail
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...>
54 template<class T1, class T2, class... T>
55 struct common_type<T1, T2, T...>: common_type<typename common_type<T1, T2>::type, T...>
59 #endif // !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES)
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
68 struct common_type: common_type<typename common_type<T1, T2>::type, T3, T4, T5, T6, T7, T8, T9>
72 #endif // !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
76 template<class T> struct common_type<T>: boost::decay<T>
82 namespace type_traits_detail
87 #if !defined(BOOST_NO_CXX11_DECLTYPE)
89 #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
91 #if !defined(BOOST_MSVC) || BOOST_MSVC > 1800
93 // internal compiler error on msvc-12.0
95 template<class T1, class T2> using builtin_common_type = typename boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )>::type;
97 template<class T1, class T2> struct common_type_impl: mp_defer<builtin_common_type, T1, T2>
103 template<class T1, class T2> using builtin_common_type = decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() );
105 template<class T1, class T2> struct common_type_impl_2: mp_defer<builtin_common_type, T1, T2>
109 template<class T1, class T2> using decay_common_type = typename boost::decay<typename common_type_impl_2<T1, T2>::type>::type;
111 template<class T1, class T2> struct common_type_impl: mp_defer<decay_common_type, T1, T2>
115 #endif // !defined(BOOST_MSVC) || BOOST_MSVC > 1800
119 template<class T1, class T2> struct common_type_impl: boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )>
123 #endif // #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
125 #endif // #if !defined(BOOST_NO_CXX11_DECLTYPE)
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>
133 template<class T1, class T2> struct common_type_decay_helper<T1, T2, T1, T2>: common_type_impl<T1, T2>
137 } // type_traits_detail
139 template<class T1, class T2> struct common_type<T1, T2>: type_traits_detail::common_type_decay_helper<T1, T2>
145 #endif // #ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED