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