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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 | |
56 | empty(Sequence const&) | |
57 | { | |
58 | typedef typename result_of::empty<Sequence>::type result; | |
59 | return result(); | |
60 | } | |
61 | }} | |
62 | ||
63 | #endif |