#ifndef BOOST_MPL_MAP_AUX_AT_IMPL_HPP_INCLUDED

#define BOOST_MPL_MAP_AUX_AT_IMPL_HPP_INCLUDED

// Copyright Aleksey Gurtovoy 2003-2004

// Copyright David Abrahams 2003-2004

//

// 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)

//

// See http://www.boost.org/libs/mpl for documentation.

// $Source: /cvsroot/boost/boost/boost/mpl/map/aux_/at_impl.hpp,v $

// $Date: 2005/12/05 17:59:21 $

// $Revision: 1.7 $

#include <boost/mpl/at_fwd.hpp>

#include <boost/mpl/long.hpp>

#include <boost/mpl/map/aux_/tag.hpp>

#include <boost/mpl/aux_/order_impl.hpp>

#include <boost/mpl/aux_/overload_names.hpp>

#include <boost/mpl/aux_/type_wrapper.hpp>

#include <boost/mpl/aux_/ptr_to_ref.hpp>

#include <boost/mpl/aux_/static_cast.hpp>

#include <boost/mpl/aux_/config/typeof.hpp>

#include <boost/mpl/aux_/config/ctps.hpp>

#if !defined(BOOST_MPL_CFG_TYPEOF_BASED_SEQUENCES)

#   include <boost/mpl/eval_if.hpp>

#   include <boost/mpl/pair.hpp>

#   include <boost/mpl/void.hpp>

#   include <boost/mpl/aux_/config/static_constant.hpp>

#endif

namespace boost { namespace mpl {

#if defined(BOOST_MPL_CFG_TYPEOF_BASED_SEQUENCES)

template< typename Map, typename Key >

struct m_at

{

    typedef aux::type_wrapper<Key> key_;

    typedef __typeof__( BOOST_MPL_AUX_OVERLOAD_CALL_VALUE_BY_KEY(

          Map

        , BOOST_MPL_AUX_STATIC_CAST(key_*, 0)

        ) ) type;

};

template<>

struct at_impl< aux::map_tag >

{

    template< typename Map, typename Key > struct apply

        : aux::wrapped_type< typename m_at<

              Map

            , Key

            >::type >

    {

    };

};

// agurt 31/jan/04: two-step implementation for the sake of GCC 3.x

template< typename Map, long order > 

struct item_by_order_impl

{

    typedef __typeof__( BOOST_MPL_AUX_OVERLOAD_CALL_ITEM_BY_ORDER(

          Map 

        , BOOST_MPL_AUX_STATIC_CAST(long_<order>*, 0)

        ) ) type;

};

template< typename Map, long order >

struct item_by_order

    : aux::wrapped_type<

          typename item_by_order_impl<Map,order>::type

        >

{

};

#else // BOOST_MPL_CFG_TYPEOF_BASED_SEQUENCES

#   if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)

template< typename Map, long n > struct m_at

{

    typedef void_ type;

};

#   else

template< long n > struct m_at_impl

{

    template< typename Map > struct result_

    {

        typedef void_ type;

    };

};

template< typename Map, long n > struct m_at

{

    typedef typename m_at_impl<n>::result_<Map>::type type;

};

#   endif

template<>

struct at_impl< aux::map_tag >

{

    template< typename Map, typename Key > struct apply

    {

        typedef typename m_at< Map, (x_order_impl<Map,Key>::value - 2) >::type item_;       

        typedef typename eval_if<

              is_void_<item_>

            , void_

            , second<item_>

            >::type type;

    };

};

template< typename Map, long order > struct is_item_masked

{

    BOOST_STATIC_CONSTANT(bool, value = 

          sizeof( BOOST_MPL_AUX_OVERLOAD_CALL_IS_MASKED(

              Map

            , BOOST_MPL_AUX_STATIC_CAST(long_<order>*, 0)

            ) ) == sizeof(aux::yes_tag)

        );

};

template< typename Map, long order > struct item_by_order

{    

    typedef typename eval_if_c< 

          is_item_masked<Map,order>::value

        , void_

        , m_at<Map,(order - 2)>

        >::type type;

};

#endif

}}

#endif // BOOST_MPL_SET_AUX_AT_IMPL_HPP_INCLUDED