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/iterator/detail/config_def.hpp> 11 12 # include <boost/detail/workaround.hpp> 13 14 # include <boost/mpl/eval_if.hpp> 15 # include <boost/mpl/identity.hpp> 16 # include <boost/mpl/placeholders.hpp> 17 # include <boost/mpl/aux_/lambda_support.hpp> 18 19 # include <boost/type_traits/is_convertible.hpp> 20 21 # include <boost/static_assert.hpp> 22 23 #include <iterator> 24 25 namespace boost { 26 namespace iterators { 27 28 // 29 // Traversal Categories 30 // 31 32 struct no_traversal_tag {}; 33 34 struct incrementable_traversal_tag 35 : no_traversal_tag 36 { 37 // incrementable_traversal_tag() {} 38 // incrementable_traversal_tag(std::output_iterator_tag const&) {}; 39 }; 40 41 struct single_pass_traversal_tag 42 : incrementable_traversal_tag 43 { 44 // single_pass_traversal_tag() {} 45 // single_pass_traversal_tag(std::input_iterator_tag const&) {}; 46 }; 47 48 struct forward_traversal_tag 49 : single_pass_traversal_tag 50 { 51 // forward_traversal_tag() {} 52 // forward_traversal_tag(std::forward_iterator_tag const&) {}; 53 }; 54 55 struct bidirectional_traversal_tag 56 : forward_traversal_tag 57 { 58 // bidirectional_traversal_tag() {}; 59 // bidirectional_traversal_tag(std::bidirectional_iterator_tag const&) {}; 60 }; 61 62 struct random_access_traversal_tag 63 : bidirectional_traversal_tag 64 { 65 // random_access_traversal_tag() {}; 66 // random_access_traversal_tag(std::random_access_iterator_tag const&) {}; 67 }; 68 69 namespace detail 70 { 71 // 72 // Convert a "strictly old-style" iterator category to a traversal 73 // tag. This is broken out into a separate metafunction to reduce 74 // the cost of instantiating iterator_category_to_traversal, below, 75 // for new-style types. 76 // 77 template <class Cat> 78 struct old_category_to_traversal 79 : mpl::eval_if< 80 is_convertible<Cat,std::random_access_iterator_tag> 81 , mpl::identity<random_access_traversal_tag> 82 , mpl::eval_if< 83 is_convertible<Cat,std::bidirectional_iterator_tag> 84 , mpl::identity<bidirectional_traversal_tag> 85 , mpl::eval_if< 86 is_convertible<Cat,std::forward_iterator_tag> 87 , mpl::identity<forward_traversal_tag> 88 , mpl::eval_if< 89 is_convertible<Cat,std::input_iterator_tag> 90 , mpl::identity<single_pass_traversal_tag> 91 , mpl::eval_if< 92 is_convertible<Cat,std::output_iterator_tag> 93 , mpl::identity<incrementable_traversal_tag> 94 , void 95 > 96 > 97 > 98 > 99 > 100 {}; 101 102 } // namespace detail 103 104 // 105 // Convert an iterator category into a traversal tag 106 // 107 template <class Cat> 108 struct iterator_category_to_traversal 109 : mpl::eval_if< // if already convertible to a traversal tag, we're done. 110 is_convertible<Cat,incrementable_traversal_tag> 111 , mpl::identity<Cat> 112 , boost::iterators::detail::old_category_to_traversal<Cat> 113 > 114 {}; 115 116 // Trait to get an iterator's traversal category 117 template <class Iterator = mpl::_1> 118 struct iterator_traversal 119 : iterator_category_to_traversal< 120 typename std::iterator_traits<Iterator>::iterator_category 121 > 122 {}; 123 124 # ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT 125 // Hack because BOOST_MPL_AUX_LAMBDA_SUPPORT doesn't seem to work 126 // out well. Instantiating the nested apply template also 127 // requires instantiating iterator_traits on the 128 // placeholder. Instead we just specialize it as a metafunction 129 // class. 130 template <> 131 struct iterator_traversal<mpl::_1> 132 { 133 template <class T> 134 struct apply : iterator_traversal<T> 135 {}; 136 }; 137 template <> 138 struct iterator_traversal<mpl::_> 139 : iterator_traversal<mpl::_1> 140 {}; 141 # endif 142 143 // 144 // Convert an iterator traversal to one of the traversal tags. 145 // 146 template <class Traversal> 147 struct pure_traversal_tag 148 : mpl::eval_if< 149 is_convertible<Traversal,random_access_traversal_tag> 150 , mpl::identity<random_access_traversal_tag> 151 , mpl::eval_if< 152 is_convertible<Traversal,bidirectional_traversal_tag> 153 , mpl::identity<bidirectional_traversal_tag> 154 , mpl::eval_if< 155 is_convertible<Traversal,forward_traversal_tag> 156 , mpl::identity<forward_traversal_tag> 157 , mpl::eval_if< 158 is_convertible<Traversal,single_pass_traversal_tag> 159 , mpl::identity<single_pass_traversal_tag> 160 , mpl::eval_if< 161 is_convertible<Traversal,incrementable_traversal_tag> 162 , mpl::identity<incrementable_traversal_tag> 163 , void 164 > 165 > 166 > 167 > 168 > 169 { 170 }; 171 172 // 173 // Trait to retrieve one of the iterator traversal tags from the iterator category or traversal. 174 // 175 template <class Iterator = mpl::_1> 176 struct pure_iterator_traversal 177 : pure_traversal_tag<typename iterator_traversal<Iterator>::type> 178 {}; 179 180 # ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT 181 template <> 182 struct pure_iterator_traversal<mpl::_1> 183 { 184 template <class T> 185 struct apply : pure_iterator_traversal<T> 186 {}; 187 }; 188 template <> 189 struct pure_iterator_traversal<mpl::_> 190 : pure_iterator_traversal<mpl::_1> 191 {}; 192 # endif 193 194 } // namespace iterators 195 196 using iterators::no_traversal_tag; 197 using iterators::incrementable_traversal_tag; 198 using iterators::single_pass_traversal_tag; 199 using iterators::forward_traversal_tag; 200 using iterators::bidirectional_traversal_tag; 201 using iterators::random_access_traversal_tag; 202 using iterators::iterator_category_to_traversal; 203 using iterators::iterator_traversal; 204 205 // This import is needed for backward compatibility with Boost.Range: 206 // boost/range/detail/demote_iterator_traversal_tag.hpp 207 // It should be removed when that header is fixed. 208 namespace detail { 209 using iterators::pure_traversal_tag; 210 } // namespace detail 211 212 } // namespace boost 213 214 #include <boost/iterator/detail/config_undef.hpp> 215 216 #endif // BOOST_ITERATOR_CATEGORIES_HPP 217