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

   1 /*=============================================================================
   2     Copyright (c) 2001-2006 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 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 result_of::equal_to<first_type, last_type> equal_to;
  35
  36                 typedef typename
  37                     mpl::if_<
  38                         equal_to
  39                       , concat_type
  40                       , joint_view_iterator<first_type, last_type, concat_type>
  41                     >::type
  42                 type;
  43
  44                 static type
  45                 call(Sequence& s, mpl::true_)
  46                 {
  47                     return s.concat();
  48                 }
  49
  50                 static type
  51                 call(Sequence& s, mpl::false_)
  52                 {
  53                     return type(s.first(), s.concat());
  54                 }
  55
  56                 static type
  57                 call(Sequence& s)
  58                 {
  59                     return call(s, equal_to());
  60                 }
  61             };
  62         };
  63     }
  64 }}
  65
  66 #endif