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
33namespace boost {
34namespace iterators {
35
36// forward declaration
37struct use_default;
38
39namespace detail {
40
41struct 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//
61template <class ValueParam, class Reference>
62struct 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
83template <class Traversal, class ValueParam, class Reference>
84struct 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.
114template <class T>
115struct 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
123template <class T>
124struct 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//
134template <class Category, class Traversal>
135struct 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
157template <class Traversal, class ValueParam, class Reference>
158struct 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//
179template <class CategoryOrTraversal, class ValueParam, class Reference>
180struct 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
194