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/*!
@file
Defines `boost::hana::detail::has_[nontrivial_]common_embedding`.
@copyright Louis Dionne 2013-2017
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_DETAIL_HAS_COMMON_EMBEDDING_HPP
#define BOOST_HANA_DETAIL_HAS_COMMON_EMBEDDING_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/common.hpp>
#include <boost/hana/core/to.hpp>
#include <boost/hana/detail/void_t.hpp>
#include <type_traits>
BOOST_HANA_NAMESPACE_BEGIN namespace detail {
template <template <typename...> class Concept, typename T, typename U, typename = void>
struct has_common_embedding_impl : std::false_type { };
template <template <typename...> class Concept, typename T, typename U>
struct has_common_embedding_impl<Concept, T, U, detail::void_t<
typename common<T, U>::type
>> {
using Common = typename common<T, U>::type;
using type = std::integral_constant<bool,
Concept<T>::value &&
Concept<U>::value &&
Concept<Common>::value &&
is_embedded<T, Common>::value &&
is_embedded<U, Common>::value
>;
};
//! @ingroup group-details
//! Returns whether `T` and `U` both have an embedding into a
//! common type.
//!
//! If `T` and `U` do not have a common-type, this metafunction returns
//! false.
template <template <typename...> class Concept, typename T, typename U>
using has_common_embedding = typename has_common_embedding_impl<Concept, T, U>::type;
template <template <typename...> class Concept, typename T, typename U>
struct has_nontrivial_common_embedding_impl
: has_common_embedding_impl<Concept, T, U>
{ };
template <template <typename...> class Concept, typename T>
struct has_nontrivial_common_embedding_impl<Concept, T, T>
: std::false_type
{ };
//! @ingroup group-details
//! Returns whether `T` and `U` are distinct and both have an embedding
//! into a common type.
//!
//! If `T` and `U` do not have a common-type, this metafunction returns
//! false.
template <template <typename...> class Concept, typename T, typename U>
using has_nontrivial_common_embedding =
typename has_nontrivial_common_embedding_impl<Concept, T, U>::type;
} BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_DETAIL_HAS_COMMON_EMBEDDING_HPP
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