Chris@16: /*=============================================================================
Chris@16:     Copyright (c) 2001-2011 Joel de Guzman
Chris@16:     Copyright (c) 2006 Dan Marsden
Chris@16: 
Chris@16:     Distributed under the Boost Software License, Version 1.0. (See accompanying 
Chris@16:     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: ==============================================================================*/
Chris@16: #if !defined(FUSION_VALUE_AT_KEY_05052005_0229)
Chris@16: #define FUSION_VALUE_AT_KEY_05052005_0229
Chris@16: 
Chris@101: #include <boost/fusion/support/config.hpp>
Chris@16: #include <boost/mpl/int.hpp>
Chris@16: #include <boost/fusion/sequence/intrinsic_fwd.hpp>
Chris@16: #include <boost/fusion/iterator/value_of_data.hpp>
Chris@16: #include <boost/fusion/algorithm/query/find.hpp>
Chris@16: #include <boost/fusion/support/tag_of.hpp>
Chris@16: 
Chris@16: namespace boost { namespace fusion
Chris@16: {
Chris@16:     // Special tags:
Chris@16:     struct sequence_facade_tag;
Chris@16:     struct boost_array_tag; // boost::array tag
Chris@16:     struct mpl_sequence_tag; // mpl sequence tag
Chris@16:     struct std_pair_tag; // std::pair tag
Chris@16: 
Chris@16:     namespace extension
Chris@16:     {
Chris@16:         template <typename Tag>
Chris@16:         struct value_at_key_impl
Chris@16:         {
Chris@16:             template <typename Seq, typename Key>
Chris@16:             struct apply
Chris@16:               : result_of::value_of_data<
Chris@16:                     typename result_of::find<Seq, Key>::type
Chris@16:                 >
Chris@16:             {};
Chris@16:         };
Chris@16: 
Chris@16:         template <>
Chris@16:         struct value_at_key_impl<sequence_facade_tag>
Chris@16:         {
Chris@16:             template <typename Sequence, typename Key>
Chris@16:             struct apply : Sequence::template value_at_key<Sequence, Key> {};
Chris@16:         };
Chris@16: 
Chris@16:         template <>
Chris@16:         struct value_at_key_impl<boost_array_tag>;
Chris@16: 
Chris@16:         template <>
Chris@16:         struct value_at_key_impl<mpl_sequence_tag>;
Chris@16: 
Chris@16:         template <>
Chris@16:         struct value_at_key_impl<std_pair_tag>;
Chris@16:     }
Chris@16:     
Chris@16:     namespace result_of
Chris@16:     {
Chris@16:         template <typename Sequence, typename N>
Chris@16:         struct value_at_key
Chris@16:             : extension::value_at_key_impl<typename detail::tag_of<Sequence>::type>::
Chris@16:                 template apply<Sequence, N>
Chris@16:         {};
Chris@16:     }
Chris@16: }}
Chris@16: 
Chris@16: #endif
Chris@16: