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

    Copyright (c) 2001-2006 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_KEY_IMPL_05222005_0254)

#define FUSION_AT_KEY_IMPL_05222005_0254



#include <boost/fusion/support/detail/access.hpp>

#include <boost/type_traits/is_const.hpp>

#include <boost/mpl/identity.hpp>



namespace boost { namespace fusion

{

    struct map_tag;



    namespace extension

    {

        template <typename Tag>

        struct at_key_impl;



        template <>

        struct at_key_impl<map_tag>

        {

            template <typename Sequence, typename Key>

            struct apply 

            {

                typedef typename Sequence::template meta_at_impl<Key> element;

                

                typedef typename

                    mpl::eval_if<

                        is_const<Sequence>

                      , detail::cref_result<element>

                      , detail::ref_result<element>

                    >::type

                type;

    

                static type

                call(Sequence& m)

                {

                    return m.at_impl(mpl::identity<Key>());

                }

            };

        };

    }

}}



#endif

