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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 | |
6 | ||
7 | # include <boost/iterator/iterator_categories.hpp> | |
8 | ||
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> | |
15 | ||
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> | |
20 | ||
21 | # include <boost/type_traits/is_same.hpp> | |
22 | ||
23 | # include <boost/iterator/detail/config_def.hpp> // try to keep this last | |
24 | ||
25 | # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY | |
26 | # include <boost/detail/indirect_traits.hpp> | |
27 | # endif | |
28 | ||
29 | // | |
30 | // iterator_category deduction for iterator_facade | |
31 | // | |
32 | ||
33 | namespace boost { | |
34 | namespace iterators { | |
35 | ||
36 | // forward declaration | |
37 | struct use_default; | |
38 | ||
39 | namespace detail { | |
40 | ||
41 | struct input_output_iterator_tag | |
42 | : std::input_iterator_tag | |
43 | { | |
44 | // Using inheritance for only input_iterator_tag helps to avoid | |
45 | // ambiguities when a stdlib implementation dispatches on a | |
46 | // function which is overloaded on both input_iterator_tag and | |
47 | // output_iterator_tag, as STLPort does, in its __valid_range | |
48 | // function. I claim it's better to avoid the ambiguity in these | |
49 | // cases. | |
50 | operator std::output_iterator_tag() const | |
51 | { | |
52 | return std::output_iterator_tag(); | |
53 | } | |
54 | }; | |
55 | ||
56 | // | |
57 | // True iff the user has explicitly disabled writability of this | |
58 | // iterator. Pass the iterator_facade's Value parameter and its | |
59 | // nested ::reference type. | |
60 | // | |
61 | template <class ValueParam, class Reference> | |
62 | struct iterator_writability_disabled | |
63 | # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY // Adding Thomas' logic? | |
64 | : mpl::or_< | |
65 | is_const<Reference> | |
66 | , boost::detail::indirect_traits::is_reference_to_const<Reference> | |
67 | , is_const<ValueParam> | |
68 | > | |
69 | # else | |
70 | : is_const<ValueParam> | |
71 | # endif | |
72 | {}; | |
73 | ||
74 | ||
75 | // | |
76 | // Convert an iterator_facade's traversal category, Value parameter, | |
77 | // and ::reference type to an appropriate old-style category. | |
78 | // | |
79 | // Due to changeset 21683, this now never results in a category convertible | |
80 | // to output_iterator_tag. | |
81 | // | |
82 | // Change at: https://svn.boost.org/trac/boost/changeset/21683 | |
83 | template <class Traversal, class ValueParam, class Reference> | |
84 | struct iterator_facade_default_category | |
85 | : mpl::eval_if< | |
86 | mpl::and_< | |
87 | is_reference<Reference> | |
88 | , is_convertible<Traversal,forward_traversal_tag> | |
89 | > | |
90 | , mpl::eval_if< | |
91 | is_convertible<Traversal,random_access_traversal_tag> | |
92 | , mpl::identity<std::random_access_iterator_tag> | |
93 | , mpl::if_< | |
94 | is_convertible<Traversal,bidirectional_traversal_tag> | |
95 | , std::bidirectional_iterator_tag | |
96 | , std::forward_iterator_tag | |
97 | > | |
98 | > | |
99 | , typename mpl::eval_if< | |
100 | mpl::and_< | |
101 | is_convertible<Traversal, single_pass_traversal_tag> | |
102 | ||
103 | // check for readability | |
104 | , is_convertible<Reference, ValueParam> | |
105 | > | |
106 | , mpl::identity<std::input_iterator_tag> | |
107 | , mpl::identity<Traversal> | |
108 | > | |
109 | > | |
110 | { | |
111 | }; | |
112 | ||
113 | // True iff T is convertible to an old-style iterator category. | |
114 | template <class T> | |
115 | struct is_iterator_category | |
116 | : mpl::or_< | |
117 | is_convertible<T,std::input_iterator_tag> | |
118 | , is_convertible<T,std::output_iterator_tag> | |
119 | > | |
120 | { | |
121 | }; | |
122 | ||
123 | template <class T> | |
124 | struct is_iterator_traversal | |
125 | : is_convertible<T,incrementable_traversal_tag> | |
126 | {}; | |
127 | ||
128 | // | |
129 | // A composite iterator_category tag convertible to Category (a pure | |
130 | // old-style category) and Traversal (a pure traversal tag). | |
131 | // Traversal must be a strict increase of the traversal power given by | |
132 | // Category. | |
133 | // | |
134 | template <class Category, class Traversal> | |
135 | struct iterator_category_with_traversal | |
136 | : Category, Traversal | |
137 | { | |
138 | // Make sure this isn't used to build any categories where | |
139 | // convertibility to Traversal is redundant. Should just use the | |
140 | // Category element in that case. | |
141 | BOOST_MPL_ASSERT_NOT(( | |
142 | is_convertible< | |
143 | typename iterator_category_to_traversal<Category>::type | |
144 | , Traversal | |
145 | >)); | |
146 | ||
147 | BOOST_MPL_ASSERT((is_iterator_category<Category>)); | |
148 | BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>)); | |
149 | BOOST_MPL_ASSERT_NOT((is_iterator_traversal<Category>)); | |
150 | # if !BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1310)) | |
151 | BOOST_MPL_ASSERT((is_iterator_traversal<Traversal>)); | |
152 | # endif | |
153 | }; | |
154 | ||
155 | // Computes an iterator_category tag whose traversal is Traversal and | |
156 | // which is appropriate for an iterator | |
157 | template <class Traversal, class ValueParam, class Reference> | |
158 | struct facade_iterator_category_impl | |
159 | { | |
160 | BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>)); | |
161 | ||
162 | typedef typename iterator_facade_default_category< | |
163 | Traversal,ValueParam,Reference | |
164 | >::type category; | |
165 | ||
166 | typedef typename mpl::if_< | |
167 | is_same< | |
168 | Traversal | |
169 | , typename iterator_category_to_traversal<category>::type | |
170 | > | |
171 | , category | |
172 | , iterator_category_with_traversal<category,Traversal> | |
173 | >::type type; | |
174 | }; | |
175 | ||
176 | // | |
177 | // Compute an iterator_category for iterator_facade | |
178 | // | |
179 | template <class CategoryOrTraversal, class ValueParam, class Reference> | |
180 | struct facade_iterator_category | |
181 | : mpl::eval_if< | |
182 | is_iterator_category<CategoryOrTraversal> | |
183 | , mpl::identity<CategoryOrTraversal> // old-style categories are fine as-is | |
184 | , facade_iterator_category_impl<CategoryOrTraversal,ValueParam,Reference> | |
185 | > | |
186 | { | |
187 | }; | |
188 | ||
189 | }}} // namespace boost::iterators::detail | |
190 | ||
191 | # include <boost/iterator/detail/config_undef.hpp> | |
192 | ||
193 | #endif // FACADE_ITERATOR_CATEGORY_DWA20031118_HPP |