map/detail/value_at_impl.hpp

0001 /*=============================================================================
0002     Copyright (c) 2001-2013 Joel de Guzman
0003
0004     Distributed under the Boost Software License, Version 1.0. (See accompanying
0005     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 ==============================================================================*/
0007 #if !defined(BOOST_FUSION_MAP_DETAIL_VALUE_AT_IMPL_02042013_0821)
0008 #define BOOST_FUSION_MAP_DETAIL_VALUE_AT_IMPL_02042013_0821
0009
0010 #include <boost/fusion/support/config.hpp>
0011 #include <boost/mpl/at.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_impl;
0022
0023         template <>
0024         struct value_at_impl<map_tag>
0025         {
0026             template <typename Sequence, typename N>
0027             struct apply
0028             {
0029                 typedef mpl::int_<N::value> index;
0030                 typedef
0031                     decltype(boost::declval<Sequence>().get_val(index()))
0032                 type;
0033             };
0034         };
0035     }
0036 }}
0037
0038 #endif
0039