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_VALUE_AT_05052005_0229) |
8 | #define FUSION_VALUE_AT_05052005_0229 |
9 | |
10 | #include <boost/fusion/support/config.hpp> |
11 | #include <boost/mpl/int.hpp> |
12 | #include <boost/mpl/if.hpp> |
13 | #include <boost/mpl/or.hpp> |
14 | #include <boost/mpl/less.hpp> |
15 | #include <boost/mpl/empty_base.hpp> |
16 | #include <boost/fusion/sequence/intrinsic_fwd.hpp> |
17 | #include <boost/fusion/support/tag_of.hpp> |
18 | #include <boost/fusion/support/category_of.hpp> |
19 | |
20 | namespace boost { namespace fusion |
21 | { |
22 | // Special tags: |
23 | struct sequence_facade_tag; |
24 | struct boost_tuple_tag; // boost::tuples::tuple tag |
25 | struct boost_array_tag; // boost::array tag |
26 | struct mpl_sequence_tag; // mpl sequence tag |
27 | struct std_pair_tag; // std::pair tag |
28 | |
29 | namespace extension |
30 | { |
31 | template <typename Tag> |
32 | struct value_at_impl |
33 | { |
34 | template <typename Sequence, typename N> |
35 | struct apply; |
36 | }; |
37 | |
38 | template <> |
39 | struct value_at_impl<sequence_facade_tag> |
40 | { |
41 | template <typename Sequence, typename N> |
42 | struct apply : Sequence::template value_at<Sequence, N> {}; |
43 | }; |
44 | |
45 | template <> |
46 | struct value_at_impl<boost_tuple_tag>; |
47 | |
48 | template <> |
49 | struct value_at_impl<boost_array_tag>; |
50 | |
51 | template <> |
52 | struct value_at_impl<mpl_sequence_tag>; |
53 | |
54 | template <> |
55 | struct value_at_impl<std_pair_tag>; |
56 | } |
57 | |
58 | namespace detail |
59 | { |
60 | template <typename Sequence, typename N, typename Tag> |
61 | struct value_at_impl |
62 | : mpl::if_< |
63 | mpl::or_< |
64 | mpl::less<N, typename extension::size_impl<Tag>::template apply<Sequence>::type> |
65 | , traits::is_unbounded<Sequence> |
66 | > |
67 | , typename extension::value_at_impl<Tag>::template apply<Sequence, N> |
68 | , mpl::empty_base |
69 | >::type |
70 | {}; |
71 | } |
72 | |
73 | namespace result_of |
74 | { |
75 | template <typename Sequence, typename N> |
76 | struct value_at |
77 | : detail::value_at_impl<Sequence, N, typename detail::tag_of<Sequence>::type> |
78 | {}; |
79 | |
80 | template <typename Sequence, int N> |
81 | struct value_at_c |
82 | : fusion::result_of::value_at<Sequence, mpl::int_<N> > |
83 | {}; |
84 | } |
85 | }} |
86 | |
87 | #endif |
88 | |
89 | |