text: /*=============================================================================
      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/fusion/support/config.hpp>
  #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>
      BOOST_FUSION_GPU_ENABLED
      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>
      BOOST_FUSION_GPU_ENABLED
      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>
      BOOST_FUSION_GPU_ENABLED
      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>
      BOOST_FUSION_GPU_ENABLED
      inline typename result_of::at_c<Sequence const, N>::type
      at_c(Sequence const& seq)
      {
          return fusion::at<mpl::int_<N> >(seq);
      }
  }}
  
  #endif
  
  