back_impl.hpp

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//-----------------------------------------------------------------------------
// boost mpl/aux_/back_impl.hpp header file
// See http://www.boost.org for updates, documentation, and revision history.
//-----------------------------------------------------------------------------
//
// Copyright (c) 2000-02
// Aleksey Gurtovoy
//
// Permission to use, copy, modify, distribute and sell this software
// and its documentation for any purpose is hereby granted without fee, 
// provided that the above copyright notice appears in all copies and 
// that both the copyright notice and this permission notice appear in 
// supporting documentation. No representations are made about the 
// suitability of this software for any purpose. It is provided "as is" 
// without express or implied warranty.

#ifndef BOOST_MPL_AUX_BACK_IMPL_HPP_INCLUDED
#define BOOST_MPL_AUX_BACK_IMPL_HPP_INCLUDED

#include "boost/mpl/begin_end.hpp"
#include "boost/mpl/prior.hpp"
#include "boost/mpl/aux_/deref_wknd.hpp"
#include "boost/mpl/aux_/traits_lambda_spec.hpp"
#include "boost/mpl/aux_/config/eti.hpp"

namespace boost {
namespace mpl {

// default implementation, requires at least bi-directional iterators;
// conrete sequences might override it by specializing either the 
// 'back_traits' or the primary 'back' template

template< typename Tag >
struct back_traits
{
    template< typename Sequence > struct algorithm
    {
        typedef typename end<Sequence>::type iter_;
#if defined(BOOST_MPL_MSVC_ETI_BUG)
        typedef typename prior<iter_>::type last_;
#else
        typedef typename iter_::prior last_;
#endif
        typedef typename BOOST_MPL_AUX_DEREF_WNKD(last_) type;
    };
};

BOOST_MPL_ALGORITM_TRAITS_LAMBDA_SPEC(1,back_traits)

} // namespace mpl
} // namespace boost

#endif // BOOST_MPL_AUX_BACK_IMPL_HPP_INCLUDED