1 /*============================================================================= 2 Copyright (c) 2001-2011 Joel de Guzman 3 4 Distributed under the Boost Software License, Version 1.0. (See accompanying 5 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 6 ==============================================================================*/ 7 #if !defined(FUSION_EMPTY_09162005_0335) 8 #define FUSION_EMPTY_09162005_0335 9 10 #include <boost/fusion/support/config.hpp> 11 #include <boost/fusion/sequence/intrinsic_fwd.hpp> 12 #include <boost/fusion/sequence/intrinsic/size.hpp> 13 #include <boost/mpl/bool.hpp> 14 #include <boost/fusion/support/tag_of.hpp> 15 16 namespace boost { namespace fusion 17 { 18 // Special tags: 19 struct sequence_facade_tag; 20 struct mpl_sequence_tag; // mpl sequence tag 21 22 namespace extension 23 { 24 template <typename Tag> 25 struct empty_impl 26 { 27 template <typename Sequence> 28 struct apply 29 : mpl::bool_<(result_of::size<Sequence>::value == 0)> 30 {}; 31 }; 32 33 template <> 34 struct empty_impl<sequence_facade_tag> 35 { 36 template <typename Sequence> 37 struct apply : Sequence::template empty<Sequence> {}; 38 }; 39 40 template <> 41 struct empty_impl<mpl_sequence_tag>; 42 } 43 44 namespace result_of 45 { 46 template <typename Sequence> 47 struct empty 48 : extension::empty_impl<typename detail::tag_of<Sequence>::type>:: 49 template apply<Sequence> 50 {}; 51 } 52 53 template <typename Sequence> 54 BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED 55 inline typename result_of::empty<Sequence>::type empty(Sequence const &)56 empty(Sequence const&) 57 { 58 typedef typename result_of::empty<Sequence>::type result; 59 return result(); 60 } 61 }} 62 63 #endif 64