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