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