/*=============================================================================

    Copyright (c) 2001-2006 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_AT_IMPL_20060124_1933)

#define FUSION_AT_IMPL_20060124_1933



#include <boost/fusion/container/vector.hpp>

#include <boost/fusion/sequence/intrinsic/at.hpp>

#include <boost/fusion/container/vector/convert.hpp>

#include <boost/fusion/algorithm/transformation/transform.hpp>

#include <boost/type_traits/remove_reference.hpp>

#include <boost/type_traits/is_reference.hpp>

#include <boost/mpl/assert.hpp>

#include <boost/fusion/support/unused.hpp>

#include <boost/mpl/eval_if.hpp>

#include <boost/mpl/identity.hpp>

#include <boost/type_traits/is_same.hpp>





namespace boost { namespace fusion 

{

    struct zip_view_tag;



    namespace detail

    {

        template<typename N>

        struct poly_at

        {

            template<typename T>

            struct result;



            template<typename N1, typename SeqRef>

            struct result<poly_at<N1>(SeqRef)>

                : mpl::eval_if<is_same<SeqRef, unused_type const&>,

                               mpl::identity<unused_type>,

                               result_of::at<typename remove_reference<SeqRef>::type, N> >

            {

                BOOST_MPL_ASSERT((is_reference<SeqRef>));

            };



            template<typename Seq>

            typename result<poly_at(Seq&)>::type

            operator()(Seq& seq) const

            {

                return fusion::at<N>(seq);

            }



            template<typename Seq>

            typename result<poly_at(Seq const&)>::type

            operator()(Seq const& seq) const

            {

                return fusion::at<N>(seq);

            }



            unused_type operator()(unused_type const&) const

            {

                return unused_type();

            }

        };

    }



    namespace extension

    {

        template<typename Tag>

        struct at_impl;



        template<>

        struct at_impl<zip_view_tag>

        {

            template<typename Seq, typename N>

            struct apply

            {

                typedef typename result_of::as_vector<

                    typename result_of::transform<

                    typename Seq::sequences, detail::poly_at<N> >::type>::type type;



                static type

                call(Seq& seq)

                {

                    return type(

                        fusion::transform(seq.sequences_, detail::poly_at<N>()));

                }

            };

        };

    }

}}



#endif

