1 /*! 2 @file 3 Defines `boost::hana::detail::has_[nontrivial_]common_embedding`. 4 5 @copyright Louis Dionne 2013-2017 6 Distributed under the Boost Software License, Version 1.0. 7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) 8 */ 9 10 #ifndef BOOST_HANA_DETAIL_HAS_COMMON_EMBEDDING_HPP 11 #define BOOST_HANA_DETAIL_HAS_COMMON_EMBEDDING_HPP 12 13 #include <boost/hana/config.hpp> 14 #include <boost/hana/core/common.hpp> 15 #include <boost/hana/core/to.hpp> 16 #include <boost/hana/detail/void_t.hpp> 17 18 #include <type_traits> 19 20 21 BOOST_HANA_NAMESPACE_BEGIN namespace detail { 22 template <template <typename...> class Concept, typename T, typename U, typename = void> 23 struct has_common_embedding_impl : std::false_type { }; 24 25 template <template <typename...> class Concept, typename T, typename U> 26 struct has_common_embedding_impl<Concept, T, U, detail::void_t< 27 typename common<T, U>::type 28 >> { 29 using Common = typename common<T, U>::type; 30 using type = std::integral_constant<bool, 31 Concept<T>::value && 32 Concept<U>::value && 33 Concept<Common>::value && 34 is_embedded<T, Common>::value && 35 is_embedded<U, Common>::value 36 >; 37 }; 38 39 //! @ingroup group-details 40 //! Returns whether `T` and `U` both have an embedding into a 41 //! common type. 42 //! 43 //! If `T` and `U` do not have a common-type, this metafunction returns 44 //! false. 45 template <template <typename...> class Concept, typename T, typename U> 46 using has_common_embedding = typename has_common_embedding_impl<Concept, T, U>::type; 47 48 template <template <typename...> class Concept, typename T, typename U> 49 struct has_nontrivial_common_embedding_impl 50 : has_common_embedding_impl<Concept, T, U> 51 { }; 52 53 template <template <typename...> class Concept, typename T> 54 struct has_nontrivial_common_embedding_impl<Concept, T, T> 55 : std::false_type 56 { }; 57 58 //! @ingroup group-details 59 //! Returns whether `T` and `U` are distinct and both have an embedding 60 //! into a common type. 61 //! 62 //! If `T` and `U` do not have a common-type, this metafunction returns 63 //! false. 64 template <template <typename...> class Concept, typename T, typename U> 65 using has_nontrivial_common_embedding = 66 typename has_nontrivial_common_embedding_impl<Concept, T, U>::type; 67 } BOOST_HANA_NAMESPACE_END 68 69 #endif // !BOOST_HANA_DETAIL_HAS_COMMON_EMBEDDING_HPP 70