1/*!
2@file
3Defines `boost::hana::detail::has_[nontrivial_]common_embedding`.
4
5Copyright Louis Dionne 2013-2022
6Distributed 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
21namespace boost { namespace hana { 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} }} // end namespace boost::hana
68
69#endif // !BOOST_HANA_DETAIL_HAS_COMMON_EMBEDDING_HPP
70

source code of boost/libs/hana/include/boost/hana/detail/has_common_embedding.hpp