boost/fusion/view/zip_view/detail/begin_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_BEGIN_IMPL_20060123_2147)
   9 #define FUSION_BEGIN_IMPL_20060123_2147
  10
  11 #include <boost/fusion/support/config.hpp>
  12 #include <boost/fusion/sequence/intrinsic/begin.hpp>
  13 #include <boost/fusion/view/zip_view/zip_view_iterator_fwd.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/type_traits/is_same.hpp>
  18 #include <boost/mpl/assert.hpp>
  19 #include <boost/mpl/eval_if.hpp>
  20 #include <boost/mpl/identity.hpp>
  21 #include <boost/fusion/support/unused.hpp>
  22
  23 namespace boost { namespace fusion {
  24
  25     struct zip_view_tag;
  26
  27     namespace detail
  28     {
  29         struct poly_begin
  30         {
  31             template<typename T>
  32             struct result;
  33
  34             template<typename SeqRef>
  35             struct result<poly_begin(SeqRef)>
  36                 : mpl::eval_if<is_same<SeqRef, unused_type const&>,
  37                                mpl::identity<unused_type>,
  38                                result_of::begin<typename remove_reference<SeqRef>::type> >
  39             {
  40                 BOOST_MPL_ASSERT((is_reference<SeqRef>));
  41             };
  42
  43             template<typename Seq>
  44             BOOST_FUSION_GPU_ENABLED
  45             typename result<poly_begin(Seq&)>::type
  46             operator()(Seq& seq) const
  47             {
  48                 return fusion::begin(seq);
  49             }
  50
  51             template<typename Seq>
  52             BOOST_FUSION_GPU_ENABLED
  53             typename result<poly_begin(Seq const&)>::type
  54             operator()(Seq const& seq) const
  55             {
  56                 return fusion::begin(seq);
  57             }
  58
  59             BOOST_FUSION_GPU_ENABLED
  60             unused_type operator()(unused_type const&) const
  61             {
  62                 return unused_type();
  63             }
  64         };
  65     }
  66
  67     namespace extension
  68     {
  69         template<typename Tag>
  70         struct begin_impl;
  71
  72         template<>
  73         struct begin_impl<zip_view_tag>
  74         {
  75             template<typename Sequence>
  76             struct apply
  77             {
  78                 typedef zip_view_iterator<
  79                     typename result_of::transform<typename Sequence::sequences, detail::poly_begin>::type,
  80                     typename Sequence::category> type;
  81
  82                 BOOST_FUSION_GPU_ENABLED
  83                 static type
  84                 call(Sequence& sequence)
  85                 {
  86                     return type(
  87                         fusion::transform(sequence.sequences_, detail::poly_begin()));
  88                 }
  89             };
  90
  91
  92
  93         };
  94     }
  95 }}
  96
  97 #endif