Chris@16: /*=============================================================================
Chris@16:     Copyright (c) 2001-2011 Joel de Guzman
Chris@16: 
Chris@16:     Distributed under the Boost Software License, Version 1.0. (See accompanying 
Chris@16:     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: ==============================================================================*/
Chris@16: #if !defined(FUSION_EMPTY_09162005_0335)
Chris@16: #define FUSION_EMPTY_09162005_0335
Chris@16: 
Chris@101: #include <boost/fusion/support/config.hpp>
Chris@16: #include <boost/fusion/sequence/intrinsic_fwd.hpp>
Chris@16: #include <boost/fusion/sequence/intrinsic/size.hpp>
Chris@16: #include <boost/mpl/bool.hpp>
Chris@16: #include <boost/fusion/support/tag_of.hpp>
Chris@16: 
Chris@16: namespace boost { namespace fusion
Chris@16: {
Chris@16:     // Special tags:
Chris@16:     struct sequence_facade_tag;
Chris@16:     struct mpl_sequence_tag; // mpl sequence tag
Chris@16: 
Chris@16:     namespace extension
Chris@16:     {
Chris@16:         template <typename Tag>
Chris@16:         struct empty_impl
Chris@16:         {
Chris@16:             template <typename Sequence>
Chris@16:             struct apply 
Chris@16:                 : mpl::bool_<(result_of::size<Sequence>::value == 0)>
Chris@16:             {};
Chris@16:         };
Chris@16: 
Chris@16:         template <>
Chris@16:         struct empty_impl<sequence_facade_tag>
Chris@16:         {
Chris@16:             template <typename Sequence>
Chris@16:             struct apply : Sequence::template empty<Sequence> {};
Chris@16:         };
Chris@16: 
Chris@16:         template <>
Chris@16:         struct empty_impl<mpl_sequence_tag>;
Chris@16:     }
Chris@16: 
Chris@16:     namespace result_of
Chris@16:     {
Chris@16:         template <typename Sequence>
Chris@16:         struct empty 
Chris@16:             : extension::empty_impl<typename detail::tag_of<Sequence>::type>::
Chris@16:                 template apply<Sequence>
Chris@16:         {};
Chris@16:     }
Chris@16: 
Chris@16:     template <typename Sequence>
Chris@101:     BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
Chris@16:     inline typename result_of::empty<Sequence>::type
Chris@16:     empty(Sequence const&)
Chris@16:     {
Chris@16:         typedef typename result_of::empty<Sequence>::type result;
Chris@16:         return result();
Chris@16:     }
Chris@16: }}
Chris@16: 
Chris@16: #endif