map/detail/value_at_key_impl.hpp

0001 /*=============================================================================
0002     Copyright (c) 2001-2013 Joel de Guzman
0003     Copyright (c) 2018 Kohei Takahashi
0004
0005     Distributed under the Boost Software License, Version 1.0. (See accompanying
0006     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0007 ==============================================================================*/
0008 #if !defined(BOOST_FUSION_MAP_DETAIL_VALUE_AT_KEY_IMPL_02042013_0821)
0009 #define BOOST_FUSION_MAP_DETAIL_VALUE_AT_KEY_IMPL_02042013_0821
0010
0011 #include <boost/fusion/support/config.hpp>
0012 #include <boost/utility/declval.hpp>
0013
0014 namespace boost { namespace fusion
0015 {
0016     struct map_tag;
0017
0018     namespace extension
0019     {
0020         template <typename Tag>
0021         struct value_at_key_impl;
0022
0023         template <>
0024         struct value_at_key_impl<map_tag>
0025         {
0026             template <typename Sequence, typename Key>
0027             struct apply : BOOST_FUSION_DECLTYPE_N3031((
0028                     boost::declval<Sequence>().get_val(mpl::identity<Key>())
0029                 ))
0030             {};
0031         };
0032     }
0033 }}
0034
0035 #endif