ceph/src/boost/libs/hana/test/concept/constant/minimal.hpp

   1 // Copyright Louis Dionne 2013-2016
   2 // Distributed under the Boost Software License, Version 1.0.
   3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   4
   5 #ifndef TEST_CONCEPT_CONSTANT_MINIMAL_HPP
   6 #define TEST_CONCEPT_CONSTANT_MINIMAL_HPP
   7
   8 #include <boost/hana/concept/constant.hpp>
   9 #include <boost/hana/core/when.hpp>
  10 #include <boost/hana/fwd/core/to.hpp>
  11 #include <boost/hana/value.hpp>
  12
  13
  14 template <typename T>
  15 struct minimal_constant_tag {
  16     using value_type = T;
  17 };
  18
  19 template <typename T, T v>
  20 struct minimal_constant {
  21     using hana_tag = minimal_constant_tag<T>;
  22     static constexpr T value_ = v;
  23 };
  24
  25 namespace boost { namespace hana {
  26     template <typename T>
  27     struct value_impl<minimal_constant_tag<T>> {
  28         template <typename N>
  29         static constexpr T apply() { return N::value_; }
  30     };
  31
  32     template <typename T, typename C>
  33     struct to_impl<minimal_constant_tag<T>, C, hana::when<
  34         hana::Constant<C>::value &&
  35         hana::is_convertible<typename C::value_type, T>::value
  36     >>
  37         : hana::embedding<hana::is_embedded<typename C::value_type, T>::value>
  38     {
  39         template <typename N>
  40         static constexpr auto apply(N const&)
  41         { return minimal_constant<T, hana::value<N>()>{}; }
  42     };
  43 }} // end namespace boost::hana
  44
  45 #endif // !TEST_CONCEPT_CONSTANT_MINIMAL_HPP