ceph/src/boost/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 2013-2017
   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 #include <type_traits>
  19
  20
  21 namespace boost { namespace hana {
  22     //! @cond
  23     template <typename T, typename>
  24     struct tag_of : tag_of<T, when<true>> { };
  25     //! @endcond
  26
  27     namespace core_detail {
  28         template <typename ...>
  29         struct is_valid { static constexpr bool value = true; };
  30     }
  31
  32     template <typename T, bool condition>
  33     struct tag_of<T, when<condition>> {
  34         using type = T;
  35     };
  36
  37     template <typename T>
  38     struct tag_of<T, when<
  39         core_detail::is_valid<typename T::hana_tag>::value
  40     >> {
  41         using type = typename T::hana_tag;
  42     };
  43
  44     template <typename T> struct tag_of<T const> : tag_of<T> { };
  45     template <typename T> struct tag_of<T volatile> : tag_of<T> { };
  46     template <typename T> struct tag_of<T const volatile> : tag_of<T> { };
  47     template <typename T> struct tag_of<T&> : tag_of<T> { };
  48     template <typename T> struct tag_of<T&&> : tag_of<T> { };
  49
  50     namespace detail {
  51         template <typename T>
  52         struct has_idempotent_tag
  53             : std::is_same<hana::tag_of_t<T>,
  54                            std::remove_const_t<std::remove_reference_t<T>>>
  55         { };
  56     }
  57 }} // end namespace boost::hana
  58
  59 #endif // !BOOST_HANA_CORE_TAG_OF_HPP