/*=============================================================================
    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_HAS_KEY_09232005_1454)
#define FUSION_HAS_KEY_09232005_1454

#include <boost/fusion/support/config.hpp>
#include <boost/fusion/sequence/intrinsic_fwd.hpp>
#include <boost/fusion/support/tag_of.hpp>
#include <boost/fusion/iterator/equal_to.hpp>
#include <boost/fusion/algorithm/query/find.hpp>
#include <boost/fusion/sequence/intrinsic/end.hpp>
#include <boost/mpl/not.hpp>

namespace boost {
namespace fusion {
struct void_;

// Special tags:
struct sequence_facade_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 has_key_impl
{
    template <typename Seq, typename Key>
    struct apply
        : mpl::not_<
          typename result_of::equal_to<
          typename result_of::find<Seq, Key>::type
        , typename result_of::end<Seq>::type
        >::type
        >::type
    {};
};

template <>
struct has_key_impl<sequence_facade_tag>
{
    template <typename Sequence, typename Key>
    struct apply : Sequence::template has_key<Sequence, Key> {};
};

template <>
struct has_key_impl<boost_array_tag>;

template <>
struct has_key_impl<mpl_sequence_tag>;

template <>
struct has_key_impl<std_pair_tag>;
}

namespace result_of {
template <typename Sequence, typename Key>
struct has_key
    : extension::has_key_impl<typename detail::tag_of<Sequence>::type>::
      template apply<Sequence, Key>
{};
}

template <typename Key, typename Sequence>
BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
inline typename result_of::has_key<Sequence, Key>::type
has_key(Sequence const&)
{
    typedef typename result_of::has_key<Sequence, Key>::type result;
    return result();
}
}
}

#endif
