boost/fusion/view/zip_view/detail/next_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_NEXT_IMPL_20060124_2006)
   9 #define FUSION_NEXT_IMPL_20060124_2006
  10
  11 #include <boost/fusion/view/zip_view/zip_view_iterator_fwd.hpp>
  12 #include <boost/fusion/iterator/next.hpp>
  13 #include <boost/fusion/algorithm/transformation/transform.hpp>
  14 #include <boost/fusion/support/unused.hpp>
  15 #include <boost/mpl/eval_if.hpp>
  16 #include <boost/mpl/identity.hpp>
  17 #include <boost/type_traits/is_same.hpp>
  18 #include <boost/type_traits/remove_reference.hpp>
  19 #include <boost/type_traits/remove_const.hpp>
  20
  21 namespace boost { namespace fusion {
  22
  23     struct zip_view_iterator_tag;
  24
  25     namespace detail
  26     {
  27         struct poly_next
  28         {
  29             template<typename Sig>
  30             struct result;
  31
  32             template<typename It>
  33             struct result<poly_next(It)>
  34             {
  35                 typedef typename remove_const<
  36                     typename remove_reference<It>::type>::type it;
  37
  38                 typedef typename mpl::eval_if<is_same<it, unused_type>,
  39                     mpl::identity<unused_type>,
  40                     result_of::next<it> >::type type;
  41             };
  42
  43             template<typename It>
  44             typename result<poly_next(It)>::type
  45             operator()(const It& it) const
  46             {
  47                 return fusion::next(it);
  48             }
  49
  50             unused_type operator()(unused_type const&) const
  51             {
  52                 return unused_type();
  53             }
  54         };
  55     }
  56
  57     namespace extension
  58     {
  59         template<typename Tag>
  60         struct next_impl;
  61
  62         template<>
  63         struct next_impl<zip_view_iterator_tag>
  64         {
  65             template<typename Iterator>
  66             struct apply
  67             {
  68                 typedef fusion::zip_view_iterator<
  69                     typename result_of::transform<typename Iterator::iterators, detail::poly_next>::type,
  70                     typename Iterator::category> type;
  71
  72                 static type
  73                 call(Iterator const& it)
  74                 {
  75                     return type(
  76                         fusion::transform(it.iterators_, detail::poly_next()));
  77                 }
  78             };
  79         };
  80     }
  81 }}
  82
  83 #endif