/*=============================================================================
    Copyright (c) 2001-2011 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_BEGIN_04052005_1132)
#define FUSION_BEGIN_04052005_1132

#include <boost/fusion/support/config.hpp>
#include <boost/utility/enable_if.hpp>
#include <boost/mpl/empty_base.hpp>
#include <boost/mpl/if.hpp>
#include <boost/fusion/sequence/intrinsic_fwd.hpp>
#include <boost/fusion/support/tag_of.hpp>
#include <boost/fusion/support/is_sequence.hpp>
#include <boost/fusion/support/is_segmented.hpp>
#include <boost/fusion/sequence/intrinsic/detail/segmented_begin.hpp>

namespace boost {
namespace fusion {
// Special tags:
struct sequence_facade_tag; // iterator facade tag
struct boost_tuple_tag; // boost::tuples::tuple tag
struct boost_array_tag; // boost::array tag
struct mpl_sequence_tag; // mpl sequence tag
struct std_pair_tag; // std::pair tag

namespace extension {
template <typename Tag>
struct begin_impl
{
    template <typename Sequence>
    struct apply
        : mpl::if_<
          traits::is_segmented<Sequence>
        , detail::segmented_begin<Sequence>
        , mpl::empty_base
        >::type
    {};
};

template <>
struct begin_impl<sequence_facade_tag>
{
    template <typename Sequence>
    struct apply : Sequence::template begin<Sequence> {};
};

template <>
struct begin_impl<boost_tuple_tag>;

template <>
struct begin_impl<boost_array_tag>;

template <>
struct begin_impl<mpl_sequence_tag>;

template <>
struct begin_impl<std_pair_tag>;
}

namespace result_of {
template <typename Sequence>
struct begin
    : extension::begin_impl<typename detail::tag_of<Sequence>::type>::
      template apply<Sequence>
{};
}

template <typename Sequence>
BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
inline typename
lazy_enable_if<
traits::is_sequence<Sequence>
, result_of::begin<Sequence>
>::type const
begin(Sequence& seq)
{
    return result_of::begin<Sequence>::call(seq);
}

template <typename Sequence>
BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
inline typename
lazy_enable_if<
traits::is_sequence<Sequence>
, result_of::begin<Sequence const>
>::type const
begin(Sequence const& seq)
{
    return result_of::begin<Sequence const>::call(seq);
}
}
}

#endif
