boost/fusion/container/list/detail/at_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_AT_IMPL_07172005_0726)
   8 #define FUSION_AT_IMPL_07172005_0726
   9
  10 #include <boost/fusion/support/detail/access.hpp>
  11 #include <boost/type_traits/is_const.hpp>
  12 #include <boost/type_traits/add_const.hpp>
  13 #include <boost/mpl/eval_if.hpp>
  14 #include <boost/mpl/bool.hpp>
  15
  16 namespace boost { namespace fusion
  17 {
  18     namespace detail
  19     {
  20         template <typename Cons>
  21         struct cons_deref
  22         {
  23             typedef typename Cons::car_type type;
  24         };
  25
  26         template <typename Cons, int I>
  27         struct cons_advance
  28         {
  29             typedef typename
  30                 cons_advance<Cons, I-1>::type::cdr_type
  31             type;
  32         };
  33
  34         template <typename Cons>
  35         struct cons_advance<Cons, 0>
  36         {
  37             typedef Cons type;
  38         };
  39
  40         template <typename Cons>
  41         struct cons_advance<Cons, 1>
  42         {
  43             typedef typename Cons::cdr_type type;
  44         };
  45
  46         template <typename Cons>
  47         struct cons_advance<Cons, 2>
  48         {
  49 #if BOOST_WORKAROUND(BOOST_MSVC, > 1400) // VC8 and above
  50             typedef typename Cons::cdr_type::cdr_type type;
  51 #else
  52             typedef typename Cons::cdr_type _a;
  53             typedef typename _a::cdr_type type;
  54 #endif
  55         };
  56
  57         template <typename Cons>
  58         struct cons_advance<Cons, 3>
  59         {
  60 #if BOOST_WORKAROUND(BOOST_MSVC, > 1400) // VC8 and above
  61             typedef typename Cons::cdr_type::cdr_type::cdr_type type;
  62 #else
  63             typedef typename Cons::cdr_type _a;
  64             typedef typename _a::cdr_type _b;
  65             typedef typename _b::cdr_type type;
  66 #endif
  67         };
  68
  69         template <typename Cons>
  70         struct cons_advance<Cons, 4>
  71         {
  72 #if BOOST_WORKAROUND(BOOST_MSVC, > 1400) // VC8 and above
  73             typedef typename Cons::cdr_type::cdr_type::cdr_type::cdr_type type;
  74 #else
  75             typedef typename Cons::cdr_type _a;
  76             typedef typename _a::cdr_type _b;
  77             typedef typename _b::cdr_type _c;
  78             typedef typename _c::cdr_type type;
  79 #endif
  80         };
  81     }
  82
  83     struct cons_tag;
  84
  85     namespace extension
  86     {
  87         template <typename Tag>
  88         struct at_impl;
  89
  90         template <>
  91         struct at_impl<cons_tag>
  92         {
  93             template <typename Sequence, typename N>
  94             struct apply
  95             {
  96                 typedef detail::cons_deref<
  97                     typename detail::cons_advance<Sequence, N::value>::type>
  98                 element;
  99
 100                 typedef typename
 101                     mpl::eval_if<
 102                         is_const<Sequence>
 103                       , detail::cref_result<element>
 104                       , detail::ref_result<element>
 105                     >::type
 106                 type;
 107
 108                 template <typename Cons, int N2>
 109                 static type
 110                 call(Cons& s, mpl::int_<N2>)
 111                 {
 112                     return call(s.cdr, mpl::int_<N2-1>());
 113                 }
 114
 115                 template <typename Cons>
 116                 static type
 117                 call(Cons& s, mpl::int_<0>)
 118                 {
 119                     return s.car;
 120                 }
 121
 122                 static type
 123                 call(Sequence& s)
 124                 {
 125                     return call(s, mpl::int_<N::value>());
 126                 }
 127             };
 128         };
 129     }
 130 }}
 131
 132 #endif