ceph/src/boost/libs/hana/include/boost/hana/detail/has_common_embedding.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::detail::has_[nontrivial_]common_embedding`.
   4
   5 @copyright Louis Dionne 2013-2016
   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