1 /*=============================================================================
2     Copyright (c) 2001-2011 Joel de Guzman
3     Copyright (c) 2006 Dan Marsden
4 
5     Distributed under the Boost Software License, Version 1.0. (See accompanying
6     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7 ==============================================================================*/
8 #if !defined(FUSION_AT_IMPL_20060124_1933)
9 #define FUSION_AT_IMPL_20060124_1933
10 
11 #include <boost/fusion/support/config.hpp>
12 #include <boost/fusion/container/vector.hpp>
13 #include <boost/fusion/sequence/intrinsic/at.hpp>
14 #include <boost/fusion/container/vector/convert.hpp>
15 #include <boost/fusion/algorithm/transformation/transform.hpp>
16 #include <boost/type_traits/remove_reference.hpp>
17 #include <boost/type_traits/is_reference.hpp>
18 #include <boost/mpl/assert.hpp>
19 #include <boost/fusion/support/unused.hpp>
20 #include <boost/mpl/eval_if.hpp>
21 #include <boost/mpl/identity.hpp>
22 #include <boost/type_traits/is_same.hpp>
23 
24 
25 namespace boost { namespace fusion
26 {
27     struct zip_view_tag;
28 
29     namespace detail
30     {
31         template<typename N>
32         struct poly_at
33         {
34             template<typename T>
35             struct result;
36 
37             template<typename N1, typename SeqRef>
38             struct result<poly_at<N1>(SeqRef)>
39                 : mpl::eval_if<is_same<SeqRef, unused_type const&>,
40                                mpl::identity<unused_type>,
41                                result_of::at<typename remove_reference<SeqRef>::type, N> >
42             {
43                 BOOST_MPL_ASSERT((is_reference<SeqRef>));
44             };
45 
46             template<typename Seq>
47             BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
48             typename result<poly_at(Seq&)>::type
operator ()boost::fusion::detail::poly_at49             operator()(Seq& seq) const
50             {
51                 return fusion::at<N>(seq);
52             }
53 
54             template<typename Seq>
55             BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
56             typename result<poly_at(Seq const&)>::type
operator ()boost::fusion::detail::poly_at57             operator()(Seq const& seq) const
58             {
59                 return fusion::at<N>(seq);
60             }
61 
62             BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
operator ()boost::fusion::detail::poly_at63             unused_type operator()(unused_type const&) const
64             {
65                 return unused_type();
66             }
67         };
68     }
69 
70     namespace extension
71     {
72         template<typename Tag>
73         struct at_impl;
74 
75         template<>
76         struct at_impl<zip_view_tag>
77         {
78             template<typename Seq, typename N>
79             struct apply
80             {
81                 typedef typename result_of::as_vector<
82                     typename result_of::transform<
83                     typename Seq::sequences, detail::poly_at<N> >::type>::type type;
84 
85                 BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
86                 static type
callboost::fusion::extension::at_impl::apply87                 call(Seq& seq)
88                 {
89                     return type(
90                         fusion::transform(seq.sequences_, detail::poly_at<N>()));
91                 }
92             };
93         };
94     }
95 }}
96 
97 #endif
98