1 /*=============================================================================
2     Copyright (c) 2001-2006 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/sequence/intrinsic/size.hpp>
11 #include <boost/mpl/bool.hpp>
12 #include <boost/fusion/support/tag_of.hpp>
13 
14 namespace boost { namespace fusion
15 {
16     // Special tags:
17     struct sequence_facade_tag;
18     struct mpl_sequence_tag; // mpl sequence tag
19 
20     namespace extension
21     {
22         template <typename Tag>
23         struct empty_impl
24         {
25             template <typename Sequence>
26             struct apply
27                 : mpl::bool_<(result_of::size<Sequence>::value == 0)>
28             {};
29         };
30 
31         template <>
32         struct empty_impl<sequence_facade_tag>
33         {
34             template <typename Sequence>
35             struct apply : Sequence::template empty<Sequence> {};
36         };
37 
38         template <>
39         struct empty_impl<mpl_sequence_tag>;
40     }
41 
42     namespace result_of
43     {
44         template <typename Sequence>
45         struct empty
46             : extension::empty_impl<typename detail::tag_of<Sequence>::type>::
47                 template apply<Sequence>
48         {};
49     }
50 
51     template <typename Sequence>
52     inline typename result_of::empty<Sequence>::type
empty(Sequence const &)53     empty(Sequence const&)
54     {
55         typedef typename result_of::empty<Sequence>::type result;
56         return result();
57     }
58 }}
59 
60 #endif
61