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
16namespace 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
64

source code of include/boost/fusion/sequence/intrinsic/empty.hpp