boost/fusion/view/zip_view/detail/at_impl.hpp

   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/container/vector.hpp>
  12 #include <boost/fusion/sequence/intrinsic/at.hpp>
  13 #include <boost/fusion/container/vector/convert.hpp>
  14 #include <boost/fusion/algorithm/transformation/transform.hpp>
  15 #include <boost/type_traits/remove_reference.hpp>
  16 #include <boost/type_traits/is_reference.hpp>
  17 #include <boost/mpl/assert.hpp>
  18 #include <boost/fusion/support/unused.hpp>
  19 #include <boost/mpl/eval_if.hpp>
  20 #include <boost/mpl/identity.hpp>
  21 #include <boost/type_traits/is_same.hpp>
  22
  23
  24 namespace boost { namespace fusion
  25 {
  26     struct zip_view_tag;
  27
  28     namespace detail
  29     {
  30         template<typename N>
  31         struct poly_at
  32         {
  33             template<typename T>
  34             struct result;
  35
  36             template<typename N1, typename SeqRef>
  37             struct result<poly_at<N1>(SeqRef)>
  38                 : mpl::eval_if<is_same<SeqRef, unused_type const&>,
  39                                mpl::identity<unused_type>,
  40                                result_of::at<typename remove_reference<SeqRef>::type, N> >
  41             {
  42                 BOOST_MPL_ASSERT((is_reference<SeqRef>));
  43             };
  44
  45             template<typename Seq>
  46             typename result<poly_at(Seq&)>::type
  47             operator()(Seq& seq) const
  48             {
  49                 return fusion::at<N>(seq);
  50             }
  51
  52             template<typename Seq>
  53             typename result<poly_at(Seq const&)>::type
  54             operator()(Seq const& seq) const
  55             {
  56                 return fusion::at<N>(seq);
  57             }
  58
  59             unused_type operator()(unused_type const&) const
  60             {
  61                 return unused_type();
  62             }
  63         };
  64     }
  65
  66     namespace extension
  67     {
  68         template<typename Tag>
  69         struct at_impl;
  70
  71         template<>
  72         struct at_impl<zip_view_tag>
  73         {
  74             template<typename Seq, typename N>
  75             struct apply
  76             {
  77                 typedef typename result_of::as_vector<
  78                     typename result_of::transform<
  79                     typename Seq::sequences, detail::poly_at<N> >::type>::type type;
  80
  81                 static type
  82                 call(Seq& seq)
  83                 {
  84                     return type(
  85                         fusion::transform(seq.sequences_, detail::poly_at<N>()));
  86                 }
  87             };
  88         };
  89     }
  90 }}
  91
  92 #endif