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_VALUE_AT_IMPL_20060124_2129)
9#define FUSION_VALUE_AT_IMPL_20060124_2129
10
11#include <boost/fusion/support/config.hpp>
12#include <boost/fusion/container/vector/convert.hpp>
13#include <boost/fusion/algorithm/transformation/transform.hpp>
14#include <boost/fusion/sequence/intrinsic/value_at.hpp>
15#include <boost/type_traits/remove_reference.hpp>
16#include <boost/fusion/support/unused.hpp>
17#include <boost/mpl/eval_if.hpp>
18#include <boost/mpl/identity.hpp>
19#include <boost/type_traits/is_same.hpp>
20#include <boost/config.hpp>
21
22namespace boost { namespace fusion {
23
24 struct zip_view_tag;
25
26 namespace detail
27 {
28 template<typename N>
29 struct poly_value_at
30 {
31 template<typename T>
32 struct result;
33
34 template<typename N1, typename Seq>
35 struct result<poly_value_at<N1>(Seq)>
36 : mpl::eval_if<is_same<Seq, unused_type const&>,
37 mpl::identity<unused_type>,
38 result_of::value_at<typename remove_reference<Seq>::type, N> >
39 {};
40
41 // never called, but needed for decltype-based result_of (C++0x)
42#ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
43 template<typename Seq>
44 BOOST_FUSION_GPU_ENABLED
45 typename result<poly_value_at(Seq)>::type
46 operator()(Seq&&) const;
47#endif
48 };
49 }
50
51 namespace extension
52 {
53 template<typename Tag>
54 struct value_at_impl;
55
56 template<>
57 struct value_at_impl<zip_view_tag>
58 {
59 template<typename Sequence, typename N>
60 struct apply
61 {
62 typedef typename result_of::transform<
63 typename Sequence::sequences,
64 detail::poly_value_at<N> >::type values;
65 typedef typename result_of::as_vector<values>::type type;
66 };
67 };
68 }
69}}
70
71#endif
72