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