boost/fusion/sequence/intrinsic/empty.hpp
/*=============================================================================
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