ceph/src/boost/libs/hana/include/boost/hana/core/tag_of.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::tag_of` and `boost::hana::tag_of_t`.
   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_CORE_TAG_OF_HPP
  11 #define BOOST_HANA_CORE_TAG_OF_HPP
  12
  13 #include <boost/hana/fwd/core/tag_of.hpp>
  14
  15 #include <boost/hana/config.hpp>
  16 #include <boost/hana/core/when.hpp>
  17
  18
  19 BOOST_HANA_NAMESPACE_BEGIN
  20     //! @cond
  21     template <typename T, typename>
  22     struct tag_of : tag_of<T, when<true>> { };
  23     //! @endcond
  24
  25     namespace core_detail {
  26         template <typename ...>
  27         struct is_valid { static constexpr bool value = true; };
  28     }
  29
  30     template <typename T, bool condition>
  31     struct tag_of<T, when<condition>> {
  32         using type = T;
  33     };
  34
  35     template <typename T>
  36     struct tag_of<T, when<
  37         core_detail::is_valid<typename T::hana_tag>::value
  38     >> {
  39         using type = typename T::hana_tag;
  40     };
  41
  42     template <typename T> struct tag_of<T const> : tag_of<T> { };
  43     template <typename T> struct tag_of<T volatile> : tag_of<T> { };
  44     template <typename T> struct tag_of<T const volatile> : tag_of<T> { };
  45     template <typename T> struct tag_of<T&> : tag_of<T> { };
  46     template <typename T> struct tag_of<T&&> : tag_of<T> { };
  47 BOOST_HANA_NAMESPACE_END
  48
  49 #endif // !BOOST_HANA_CORE_TAG_OF_HPP