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+/*=============================================================================
+ Copyright (c) 2001-2011 Joel de Guzman
+
+ 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_AT_05042005_0722)
+#define FUSION_AT_05042005_0722
+
+#include <boost/mpl/int.hpp>
+#include <boost/type_traits/is_const.hpp>
+#include <boost/fusion/sequence/intrinsic_fwd.hpp>
+#include <boost/fusion/support/tag_of.hpp>
+#include <boost/fusion/support/detail/access.hpp>
+
+namespace boost { namespace fusion
+{
+ // Special tags:
+ struct sequence_facade_tag;
+ struct boost_tuple_tag; // boost::tuples::tuple tag
+ struct boost_array_tag; // boost::array tag
+ struct mpl_sequence_tag; // mpl sequence tag
+ struct std_pair_tag; // std::pair tag
+ struct std_tuple_tag; // std::tuple tag
+
+ namespace extension
+ {
+ template <typename Tag>
+ struct at_impl
+ {
+ template <typename Sequence, typename N>
+ struct apply;
+ };
+
+ template <>
+ struct at_impl<sequence_facade_tag>
+ {
+ template <typename Sequence, typename N>
+ struct apply : Sequence::template at<Sequence, N> {};
+ };
+
+ template <>
+ struct at_impl<boost_tuple_tag>;
+
+ template <>
+ struct at_impl<boost_array_tag>;
+
+ template <>
+ struct at_impl<mpl_sequence_tag>;
+
+ template <>
+ struct at_impl<std_pair_tag>;
+
+ template <>
+ struct at_impl<std_tuple_tag>;
+ }
+
+ namespace result_of
+ {
+ template <typename Sequence, typename N>
+ struct at
+ : extension::at_impl<typename detail::tag_of<Sequence>::type>::
+ template apply<Sequence, N>
+ {};
+
+ template <typename Sequence, int N>
+ struct at_c
+ : at<Sequence, mpl::int_<N> >
+ {};
+ }
+
+
+ template <typename N, typename Sequence>
+ inline typename
+ lazy_disable_if<
+ is_const<Sequence>
+ , result_of::at<Sequence, N>
+ >::type
+ at(Sequence& seq)
+ {
+ return result_of::at<Sequence, N>::call(seq);
+ }
+
+ template <typename N, typename Sequence>
+ inline typename result_of::at<Sequence const, N>::type
+ at(Sequence const& seq)
+ {
+ return result_of::at<Sequence const, N>::call(seq);
+ }
+
+ template <int N, typename Sequence>
+ inline typename
+ lazy_disable_if<
+ is_const<Sequence>
+ , result_of::at_c<Sequence, N>
+ >::type
+ at_c(Sequence& seq)
+ {
+ return fusion::at<mpl::int_<N> >(seq);
+ }
+
+ template <int N, typename Sequence>
+ inline typename result_of::at_c<Sequence const, N>::type
+ at_c(Sequence const& seq)
+ {
+ return fusion::at<mpl::int_<N> >(seq);
+ }
+}}
+
+#endif
+