1 // Copyright David Abrahams 2003. Use, modification and distribution is
2 // subject to the Boost Software License, Version 1.0. (See accompanying
3 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
4 #ifndef FACADE_ITERATOR_CATEGORY_DWA20031118_HPP
5 # define FACADE_ITERATOR_CATEGORY_DWA20031118_HPP
7 # include <boost/iterator/iterator_categories.hpp>
9 # include <boost/mpl/or.hpp> // used in iterator_tag inheritance logic
10 # include <boost/mpl/and.hpp>
11 # include <boost/mpl/if.hpp>
12 # include <boost/mpl/eval_if.hpp>
13 # include <boost/mpl/identity.hpp>
14 # include <boost/mpl/assert.hpp>
16 # include <boost/type_traits/is_same.hpp>
17 # include <boost/type_traits/is_const.hpp>
18 # include <boost/type_traits/is_reference.hpp>
19 # include <boost/type_traits/is_convertible.hpp>
21 # include <boost/type_traits/is_same.hpp>
23 # include <boost/iterator/detail/config_def.hpp> // try to keep this last
25 # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY
26 # include <boost/detail/indirect_traits.hpp>
30 // iterator_category deduction for iterator_facade
33 // forward declaration
34 namespace boost { struct use_default; }
36 namespace boost { namespace detail {
38 struct input_output_iterator_tag
39 : std::input_iterator_tag
41 // Using inheritance for only input_iterator_tag helps to avoid
42 // ambiguities when a stdlib implementation dispatches on a
43 // function which is overloaded on both input_iterator_tag and
44 // output_iterator_tag, as STLPort does, in its __valid_range
45 // function. I claim it's better to avoid the ambiguity in these
47 operator std::output_iterator_tag() const
49 return std::output_iterator_tag();
54 // True iff the user has explicitly disabled writability of this
55 // iterator. Pass the iterator_facade's Value parameter and its
56 // nested ::reference type.
58 template <class ValueParam, class Reference>
59 struct iterator_writability_disabled
60 # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY // Adding Thomas' logic?
63 , boost::detail::indirect_traits::is_reference_to_const<Reference>
64 , is_const<ValueParam>
67 : is_const<ValueParam>
73 // Convert an iterator_facade's traversal category, Value parameter,
74 // and ::reference type to an appropriate old-style category.
76 // If writability has been disabled per the above metafunction, the
77 // result will not be convertible to output_iterator_tag.
79 // Otherwise, if Traversal == single_pass_traversal_tag, the following
80 // conditions will result in a tag that is convertible both to
81 // input_iterator_tag and output_iterator_tag:
83 // 1. Reference is a reference to non-const
84 // 2. Reference is not a reference and is convertible to Value
86 template <class Traversal, class ValueParam, class Reference>
87 struct iterator_facade_default_category
90 is_reference<Reference>
91 , is_convertible<Traversal,forward_traversal_tag>
94 is_convertible<Traversal,random_access_traversal_tag>
95 , mpl::identity<std::random_access_iterator_tag>
97 is_convertible<Traversal,bidirectional_traversal_tag>
98 , std::bidirectional_iterator_tag
99 , std::forward_iterator_tag
102 , typename mpl::eval_if<
104 is_convertible<Traversal, single_pass_traversal_tag>
106 // check for readability
107 , is_convertible<Reference, ValueParam>
109 , mpl::identity<std::input_iterator_tag>
110 , mpl::identity<Traversal>
116 // True iff T is convertible to an old-style iterator category.
118 struct is_iterator_category
120 is_convertible<T,std::input_iterator_tag>
121 , is_convertible<T,std::output_iterator_tag>
127 struct is_iterator_traversal
128 : is_convertible<T,incrementable_traversal_tag>
132 // A composite iterator_category tag convertible to Category (a pure
133 // old-style category) and Traversal (a pure traversal tag).
134 // Traversal must be a strict increase of the traversal power given by
137 template <class Category, class Traversal>
138 struct iterator_category_with_traversal
139 : Category, Traversal
141 # if !BOOST_WORKAROUND(BOOST_MSVC, <= 1300)
142 // Make sure this isn't used to build any categories where
143 // convertibility to Traversal is redundant. Should just use the
144 // Category element in that case.
145 BOOST_MPL_ASSERT_NOT((
147 typename iterator_category_to_traversal<Category>::type
151 BOOST_MPL_ASSERT((is_iterator_category<Category>));
152 BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>));
153 BOOST_MPL_ASSERT_NOT((is_iterator_traversal<Category>));
154 # if !BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1310))
155 BOOST_MPL_ASSERT((is_iterator_traversal<Traversal>));
160 // Computes an iterator_category tag whose traversal is Traversal and
161 // which is appropriate for an iterator
162 template <class Traversal, class ValueParam, class Reference>
163 struct facade_iterator_category_impl
165 # if !BOOST_WORKAROUND(BOOST_MSVC, <= 1300)
166 BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>));
169 typedef typename iterator_facade_default_category<
170 Traversal,ValueParam,Reference
173 typedef typename mpl::if_<
176 , typename iterator_category_to_traversal<category>::type
179 , iterator_category_with_traversal<category,Traversal>
184 // Compute an iterator_category for iterator_facade
186 template <class CategoryOrTraversal, class ValueParam, class Reference>
187 struct facade_iterator_category
189 is_iterator_category<CategoryOrTraversal>
190 , mpl::identity<CategoryOrTraversal> // old-style categories are fine as-is
191 , facade_iterator_category_impl<CategoryOrTraversal,ValueParam,Reference>
196 }} // namespace boost::detail
198 # include <boost/iterator/detail/config_undef.hpp>
200 #endif // FACADE_ITERATOR_CATEGORY_DWA20031118_HPP