deref_impl.hpp

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/*=============================================================================
    Copyright (c) 2005 Joel de Guzman
    Copyright (c) 2005 Eric Niebler

    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_DEREF_IMPL_07172005_0831)
#define FUSION_DEREF_IMPL_07172005_0831

#include <boost/mpl/eval_if.hpp>
#include <boost/type_traits/is_const.hpp>
#include <boost/type_traits/add_const.hpp>
#include <boost/type_traits/add_reference.hpp>

namespace boost { namespace fusion
{
    struct cons_iterator_tag;

    namespace extension
    {
        template <typename Tag>
        struct deref_impl;

        template <>
        struct deref_impl<cons_iterator_tag>
        {
            template <typename Iterator>
            struct apply 
            {
                typedef typename Iterator::cons_type cons_type;
                typedef typename cons_type::car_type value_type;
    
                typedef typename mpl::eval_if<
                    is_const<cons_type>
                  , add_reference<typename add_const<value_type>::type>
                  , add_reference<value_type> >::type
                type;
    
                static type
                call(Iterator const& i)
                {
                    return i.cons.car;
                }
            };
        };
    }
}}

#endif