boost/fusion/view/joint_view/detail/begin_impl.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2011 Joel de Guzman
   3
   4     Distributed under the Boost Software License, Version 1.0. (See accompanying
   5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 ==============================================================================*/
   7 #if !defined(FUSION_BEGIN_IMPL_07162005_0115)
   8 #define FUSION_BEGIN_IMPL_07162005_0115
   9
  10 #include <boost/fusion/iterator/equal_to.hpp>
  11 #include <boost/mpl/if.hpp>
  12
  13 namespace boost { namespace fusion
  14 {
  15     struct joint_view_tag;
  16
  17     template <typename Category, typename First, typename Last, typename Concat>
  18     struct joint_view_iterator;
  19
  20     namespace extension
  21     {
  22         template <typename Tag>
  23         struct begin_impl;
  24
  25         template <>
  26         struct begin_impl<joint_view_tag>
  27         {
  28             template <typename Sequence>
  29             struct apply
  30             {
  31                 typedef typename Sequence::first_type first_type;
  32                 typedef typename Sequence::last_type last_type;
  33                 typedef typename Sequence::concat_type concat_type;
  34                 typedef typename Sequence::category category;
  35                 typedef result_of::equal_to<first_type, last_type> equal_to;
  36
  37                 typedef typename
  38                     mpl::if_<
  39                         equal_to
  40                       , concat_type
  41                       , joint_view_iterator<category, first_type, last_type, concat_type>
  42                     >::type
  43                 type;
  44
  45                 static type
  46                 call(Sequence& s, mpl::true_)
  47                 {
  48                     return s.concat();
  49                 }
  50
  51                 static type
  52                 call(Sequence& s, mpl::false_)
  53                 {
  54                     return type(s.first(), s.concat());
  55                 }
  56
  57                 static type
  58                 call(Sequence& s)
  59                 {
  60                     return call(s, equal_to());
  61                 }
  62             };
  63         };
  64     }
  65 }}
  66
  67 #endif