/*=============================================================================
    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_EMPTY_09162005_0335)
#define FUSION_EMPTY_09162005_0335

#include <boost/fusion/support/config.hpp>
#include <boost/fusion/sequence/intrinsic_fwd.hpp>
#include <boost/fusion/sequence/intrinsic/size.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/fusion/support/tag_of.hpp>

namespace boost {
namespace fusion {
// Special tags:
struct sequence_facade_tag;
struct mpl_sequence_tag; // mpl sequence tag

namespace extension {
template <typename Tag>
struct empty_impl
{
    template <typename Sequence>
    struct apply
    : mpl::bool_<(result_of::size<Sequence>::value == 0)>
      {};
};

template <>
struct empty_impl<sequence_facade_tag>
{
    template <typename Sequence>
    struct apply : Sequence::template empty<Sequence> {};
};

template <>
struct empty_impl<mpl_sequence_tag>;
}

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

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

#endif
