/*=============================================================================
    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_DISTANCE_09172005_0721)
#define FUSION_DISTANCE_09172005_0721

#include <boost/fusion/support/config.hpp>
#include <boost/fusion/iterator/detail/distance.hpp>
#include <boost/fusion/support/category_of.hpp>

#include <boost/mpl/int.hpp>
#include <boost/mpl/assert.hpp>
#include <boost/type_traits/is_same.hpp>

#include <boost/fusion/support/tag_of.hpp>

namespace boost {
namespace fusion {
struct random_access_traversal_tag;

// Special tags:
struct iterator_facade_tag; // iterator facade tag
struct boost_array_iterator_tag; // boost::array iterator tag
struct mpl_iterator_tag; // mpl sequence iterator tag
struct std_pair_iterator_tag; // std::pair iterator tag

namespace extension {
template <typename Tag>
struct distance_impl
{
    // default implementation
    template <typename First, typename Last>
    struct apply : distance_detail::linear_distance<First, Last>
    {};
};

template <>
struct distance_impl<iterator_facade_tag>
{
    template <typename First, typename Last>
    struct apply : First::template distance<First, Last> {};
};

template <>
struct distance_impl<boost_array_iterator_tag>;

template <>
struct distance_impl<mpl_iterator_tag>;

template <>
struct distance_impl<std_pair_iterator_tag>;
}

namespace result_of {
template <typename First, typename Last>
struct distance
    : extension::distance_impl<typename detail::tag_of<First>::type>::
      template apply<First, Last>
{
    typedef typename extension::distance_impl<typename detail::tag_of<First>::type>::
    template apply<First, Last>::type distance_application;
    BOOST_STATIC_CONSTANT(int, value = distance_application::value);
};
}

template <typename First, typename Last>
BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
inline typename result_of::distance<First, Last>::type
distance(First const& a, Last const& b)
{
    return result_of::distance<First, Last>::call(a,b);
}
}
}

#endif
