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)
6 #ifndef BOOST_ITERATOR_CATEGORIES_HPP
7 # define BOOST_ITERATOR_CATEGORIES_HPP
9 # include <boost/config.hpp>
10 # include <boost/detail/iterator.hpp>
11 # include <boost/iterator/detail/config_def.hpp>
13 # include <boost/detail/workaround.hpp>
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>
20 # include <boost/type_traits/is_convertible.hpp>
22 # include <boost/static_assert.hpp>
28 // Traversal Categories
31 struct no_traversal_tag {};
33 struct incrementable_traversal_tag
36 // incrementable_traversal_tag() {}
37 // incrementable_traversal_tag(std::output_iterator_tag const&) {};
40 struct single_pass_traversal_tag
41 : incrementable_traversal_tag
43 // single_pass_traversal_tag() {}
44 // single_pass_traversal_tag(std::input_iterator_tag const&) {};
47 struct forward_traversal_tag
48 : single_pass_traversal_tag
50 // forward_traversal_tag() {}
51 // forward_traversal_tag(std::forward_iterator_tag const&) {};
54 struct bidirectional_traversal_tag
55 : forward_traversal_tag
57 // bidirectional_traversal_tag() {};
58 // bidirectional_traversal_tag(std::bidirectional_iterator_tag const&) {};
61 struct random_access_traversal_tag
62 : bidirectional_traversal_tag
64 // random_access_traversal_tag() {};
65 // random_access_traversal_tag(std::random_access_iterator_tag const&) {};
71 // Convert a "strictly old-style" iterator category to a traversal
72 // tag. This is broken out into a separate metafunction to reduce
73 // the cost of instantiating iterator_category_to_traversal, below,
74 // for new-style types.
77 struct old_category_to_traversal
79 is_convertible<Cat,std::random_access_iterator_tag>
80 , mpl::identity<random_access_traversal_tag>
82 is_convertible<Cat,std::bidirectional_iterator_tag>
83 , mpl::identity<bidirectional_traversal_tag>
85 is_convertible<Cat,std::forward_iterator_tag>
86 , mpl::identity<forward_traversal_tag>
88 is_convertible<Cat,std::input_iterator_tag>
89 , mpl::identity<single_pass_traversal_tag>
91 is_convertible<Cat,std::output_iterator_tag>
92 , mpl::identity<incrementable_traversal_tag>
101 } // namespace detail
104 // Convert an iterator category into a traversal tag
107 struct iterator_category_to_traversal
108 : mpl::eval_if< // if already convertible to a traversal tag, we're done.
109 is_convertible<Cat,incrementable_traversal_tag>
111 , boost::iterators::detail::old_category_to_traversal<Cat>
115 // Trait to get an iterator's traversal category
116 template <class Iterator = mpl::_1>
117 struct iterator_traversal
118 : iterator_category_to_traversal<
119 typename boost::detail::iterator_traits<Iterator>::iterator_category
123 # ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT
124 // Hack because BOOST_MPL_AUX_LAMBDA_SUPPORT doesn't seem to work
125 // out well. Instantiating the nested apply template also
126 // requires instantiating iterator_traits on the
127 // placeholder. Instead we just specialize it as a metafunction
130 struct iterator_traversal<mpl::_1>
133 struct apply : iterator_traversal<T>
137 struct iterator_traversal<mpl::_>
138 : iterator_traversal<mpl::_1>
143 // Convert an iterator traversal to one of the traversal tags.
145 template <class Traversal>
146 struct pure_traversal_tag
148 is_convertible<Traversal,random_access_traversal_tag>
149 , mpl::identity<random_access_traversal_tag>
151 is_convertible<Traversal,bidirectional_traversal_tag>
152 , mpl::identity<bidirectional_traversal_tag>
154 is_convertible<Traversal,forward_traversal_tag>
155 , mpl::identity<forward_traversal_tag>
157 is_convertible<Traversal,single_pass_traversal_tag>
158 , mpl::identity<single_pass_traversal_tag>
160 is_convertible<Traversal,incrementable_traversal_tag>
161 , mpl::identity<incrementable_traversal_tag>
172 // Trait to retrieve one of the iterator traversal tags from the iterator category or traversal.
174 template <class Iterator = mpl::_1>
175 struct pure_iterator_traversal
176 : pure_traversal_tag<typename iterator_traversal<Iterator>::type>
179 # ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT
181 struct pure_iterator_traversal<mpl::_1>
184 struct apply : pure_iterator_traversal<T>
188 struct pure_iterator_traversal<mpl::_>
189 : pure_iterator_traversal<mpl::_1>
193 } // namespace iterators
195 using iterators::no_traversal_tag;
196 using iterators::incrementable_traversal_tag;
197 using iterators::single_pass_traversal_tag;
198 using iterators::forward_traversal_tag;
199 using iterators::bidirectional_traversal_tag;
200 using iterators::random_access_traversal_tag;
201 using iterators::iterator_category_to_traversal;
202 using iterators::iterator_traversal;
204 // This import is needed for backward compatibility with Boost.Range:
205 // boost/range/detail/demote_iterator_traversal_tag.hpp
206 // It should be removed when that header is fixed.
208 using iterators::pure_traversal_tag;
209 } // namespace detail
213 #include <boost/iterator/detail/config_undef.hpp>
215 #endif // BOOST_ITERATOR_CATEGORIES_HPP