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