boost/iterator/iterator_categories.hpp

   1 // (C) Copyright Jeremy Siek 2002.
   2 // Distributed under the Boost Software License, Version 1.0. (See
   3 // accompanying file LICENSE_1_0.txt or copy at
   4 // http://www.boost.org/LICENSE_1_0.txt)
   5
   6 #ifndef BOOST_ITERATOR_CATEGORIES_HPP
   7 # define BOOST_ITERATOR_CATEGORIES_HPP
   8
   9 # include <boost/config.hpp>
  10 # include <boost/detail/iterator.hpp>
  11 # include <boost/iterator/detail/config_def.hpp>
  12
  13 # include <boost/detail/workaround.hpp>
  14
  15 # include <boost/mpl/eval_if.hpp>
  16 # include <boost/mpl/identity.hpp>
  17 # include <boost/mpl/placeholders.hpp>
  18 # include <boost/mpl/aux_/lambda_support.hpp>
  19
  20 # include <boost/type_traits/is_convertible.hpp>
  21
  22 # include <boost/static_assert.hpp>
  23
  24 namespace boost {
  25
  26 //
  27 // Traversal Categories
  28 //
  29
  30 struct no_traversal_tag {};
  31
  32 struct incrementable_traversal_tag
  33   : no_traversal_tag
  34 {
  35 //     incrementable_traversal_tag() {}
  36 //     incrementable_traversal_tag(std::output_iterator_tag const&) {};
  37 };
  38
  39 struct single_pass_traversal_tag
  40   : incrementable_traversal_tag
  41 {
  42 //     single_pass_traversal_tag() {}
  43 //     single_pass_traversal_tag(std::input_iterator_tag const&) {};
  44 };
  45
  46 struct forward_traversal_tag
  47   : single_pass_traversal_tag
  48 {
  49 //     forward_traversal_tag() {}
  50 //     forward_traversal_tag(std::forward_iterator_tag const&) {};
  51 };
  52
  53 struct bidirectional_traversal_tag
  54   : forward_traversal_tag
  55 {
  56 //     bidirectional_traversal_tag() {};
  57 //     bidirectional_traversal_tag(std::bidirectional_iterator_tag const&) {};
  58 };
  59
  60 struct random_access_traversal_tag
  61   : bidirectional_traversal_tag
  62 {
  63 //     random_access_traversal_tag() {};
  64 //     random_access_traversal_tag(std::random_access_iterator_tag const&) {};
  65 };
  66
  67 namespace detail
  68 {
  69   //
  70   // Convert a "strictly old-style" iterator category to a traversal
  71   // tag.  This is broken out into a separate metafunction to reduce
  72   // the cost of instantiating iterator_category_to_traversal, below,
  73   // for new-style types.
  74   //
  75   template <class Cat>
  76   struct old_category_to_traversal
  77     : mpl::eval_if<
  78           is_convertible<Cat,std::random_access_iterator_tag>
  79         , mpl::identity<random_access_traversal_tag>
  80         , mpl::eval_if<
  81               is_convertible<Cat,std::bidirectional_iterator_tag>
  82             , mpl::identity<bidirectional_traversal_tag>
  83             , mpl::eval_if<
  84                   is_convertible<Cat,std::forward_iterator_tag>
  85                 , mpl::identity<forward_traversal_tag>
  86                 , mpl::eval_if<
  87                       is_convertible<Cat,std::input_iterator_tag>
  88                     , mpl::identity<single_pass_traversal_tag>
  89                     , mpl::eval_if<
  90                           is_convertible<Cat,std::output_iterator_tag>
  91                         , mpl::identity<incrementable_traversal_tag>
  92                         , void
  93                       >
  94                   >
  95               >
  96           >
  97       >
  98   {};
  99
 100 # if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
 101   template <>
 102   struct old_category_to_traversal<int>
 103   {
 104       typedef int type;
 105   };
 106 # endif
 107
 108   template <class Traversal>
 109   struct pure_traversal_tag
 110     : mpl::eval_if<
 111           is_convertible<Traversal,random_access_traversal_tag>
 112         , mpl::identity<random_access_traversal_tag>
 113         , mpl::eval_if<
 114               is_convertible<Traversal,bidirectional_traversal_tag>
 115             , mpl::identity<bidirectional_traversal_tag>
 116             , mpl::eval_if<
 117                   is_convertible<Traversal,forward_traversal_tag>
 118                 , mpl::identity<forward_traversal_tag>
 119                 , mpl::eval_if<
 120                       is_convertible<Traversal,single_pass_traversal_tag>
 121                     , mpl::identity<single_pass_traversal_tag>
 122                     , mpl::eval_if<
 123                           is_convertible<Traversal,incrementable_traversal_tag>
 124                         , mpl::identity<incrementable_traversal_tag>
 125                         , void
 126                       >
 127                   >
 128               >
 129           >
 130       >
 131   {
 132   };
 133
 134 # if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
 135   template <>
 136   struct pure_traversal_tag<int>
 137   {
 138       typedef int type;
 139   };
 140 # endif
 141
 142 } // namespace detail
 143
 144
 145 //
 146 // Convert an iterator category into a traversal tag
 147 //
 148 template <class Cat>
 149 struct iterator_category_to_traversal
 150   : mpl::eval_if< // if already convertible to a traversal tag, we're done.
 151         is_convertible<Cat,incrementable_traversal_tag>
 152       , mpl::identity<Cat>
 153       , boost::detail::old_category_to_traversal<Cat>
 154     >
 155 {};
 156
 157 // Trait to get an iterator's traversal category
 158 template <class Iterator = mpl::_1>
 159 struct iterator_traversal
 160   : iterator_category_to_traversal<
 161         typename boost::detail::iterator_traits<Iterator>::iterator_category
 162     >
 163 {};
 164
 165 # ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT
 166 // Hack because BOOST_MPL_AUX_LAMBDA_SUPPORT doesn't seem to work
 167 // out well.  Instantiating the nested apply template also
 168 // requires instantiating iterator_traits on the
 169 // placeholder. Instead we just specialize it as a metafunction
 170 // class.
 171 template <>
 172 struct iterator_traversal<mpl::_1>
 173 {
 174     template <class T>
 175     struct apply : iterator_traversal<T>
 176     {};
 177 };
 178 template <>
 179 struct iterator_traversal<mpl::_>
 180   : iterator_traversal<mpl::_1>
 181 {};
 182 # endif
 183
 184 } // namespace boost
 185
 186 #include <boost/iterator/detail/config_undef.hpp>
 187
 188 #endif // BOOST_ITERATOR_CATEGORIES_HPP