boost/fusion/container/deque/detail/at_impl.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2006 Joel de Guzman
   3     Copyright (c) 2005-2006 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(BOOST_FUSION_DEQUE_AT_IMPL_09122006_2017)
   9 #define BOOST_FUSION_DEQUE_AT_IMPL_09122006_2017
  10
  11 #include <boost/fusion/container/deque/detail/keyed_element.hpp>
  12
  13 #include <boost/mpl/eval_if.hpp>
  14 #include <boost/mpl/equal_to.hpp>
  15 #include <boost/mpl/assert.hpp>
  16 #include <boost/mpl/identity.hpp>
  17
  18 #include <boost/type_traits/is_const.hpp>
  19 #include <boost/type_traits/add_const.hpp>
  20 #include <boost/type_traits/add_reference.hpp>
  21
  22 namespace boost { namespace fusion {
  23
  24     struct deque_tag;
  25
  26     namespace extension
  27     {
  28         template<typename T>
  29         struct at_impl;
  30
  31         template<>
  32         struct at_impl<deque_tag>
  33         {
  34             template<typename Sequence, typename N>
  35             struct apply
  36             {
  37                 typedef typename Sequence::next_up next_up;
  38                 typedef typename Sequence::next_down next_down;
  39                 BOOST_MPL_ASSERT_RELATION(next_down::value, !=, next_up::value);
  40
  41                 typedef mpl::plus<next_down, mpl::int_<1> > offset;
  42                 typedef mpl::int_<mpl::plus<N, offset>::value> adjusted_index;
  43                 typedef typename detail::keyed_element_value_at<Sequence, adjusted_index>::type element_type;
  44                 typedef typename add_reference<
  45                     typename mpl::eval_if<
  46                     is_const<Sequence>,
  47                     add_const<element_type>,
  48                     mpl::identity<element_type> >::type>::type type;
  49
  50                 static type call(Sequence& seq)
  51                 {
  52                     return seq.get(adjusted_index());
  53                 }
  54             };
  55         };
  56     }
  57 }}
  58
  59 #endif