1 // Types used in iterator implementation -*- C++ -*-
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51 /** @file bits/stl_iterator_base_types.h
52 * This is an internal header file, included by other library headers.
53 * Do not attempt to use it directly. @headername{iterator}
55 * This file contains all of the general iterator-related utility types,
56 * such as iterator_traits and struct iterator.
59 #ifndef _STL_ITERATOR_BASE_TYPES_H
60 #define _STL_ITERATOR_BASE_TYPES_H 1
62 #pragma GCC system_header
64 #include <bits/c++config.h>
66 #if __cplusplus >= 201103L
67 # include <type_traits> // For __void_t, is_convertible
70 #if __cplusplus > 201703L && __cpp_concepts >= 201907L
71 # include <bits/iterator_concepts.h>
74 namespace std
_GLIBCXX_VISIBILITY(default)
76 _GLIBCXX_BEGIN_NAMESPACE_VERSION
79 * @defgroup iterators Iterators
80 * Abstractions for uniform iterating through various underlying types.
85 * @defgroup iterator_tags Iterator Tags
86 * These are empty types, used to distinguish different iterators. The
87 * distinction is not made by what they contain, but simply by what they
88 * are. Different underlying algorithms can then be used based on the
89 * different operations supported by different iterator types.
92 /// Marking input iterators.
93 struct input_iterator_tag
{ };
95 /// Marking output iterators.
96 struct output_iterator_tag
{ };
98 /// Forward iterators support a superset of input iterator operations.
99 struct forward_iterator_tag
: public input_iterator_tag
{ };
101 /// Bidirectional iterators support a superset of forward iterator
103 struct bidirectional_iterator_tag
: public forward_iterator_tag
{ };
105 /// Random-access iterators support a superset of bidirectional
106 /// iterator operations.
107 struct random_access_iterator_tag
: public bidirectional_iterator_tag
{ };
109 #if __cplusplus > 201703L
110 /// Contiguous iterators point to objects stored contiguously in memory.
111 struct contiguous_iterator_tag
: public random_access_iterator_tag
{ };
116 * @brief Common %iterator class.
118 * This class does nothing but define nested typedefs. %Iterator classes
119 * can inherit from this class to save some work. The typedefs are then
120 * used in specializations and overloading.
122 * In particular, there are no default implementations of requirements
123 * such as @c operator++ and the like. (How could there be?)
125 template<typename _Category
, typename _Tp
, typename _Distance
= ptrdiff_t,
126 typename _Pointer
= _Tp
*, typename _Reference
= _Tp
&>
129 /// One of the @link iterator_tags tag types@endlink.
130 typedef _Category iterator_category
;
131 /// The type "pointed to" by the iterator.
132 typedef _Tp value_type
;
133 /// Distance between iterators is represented as this type.
134 typedef _Distance difference_type
;
135 /// This type represents a pointer-to-value_type.
136 typedef _Pointer pointer
;
137 /// This type represents a reference-to-value_type.
138 typedef _Reference reference
;
142 * @brief Traits class for iterators.
144 * This class does nothing but define nested typedefs. The general
145 * version simply @a forwards the nested typedefs from the Iterator
146 * argument. Specialized versions for pointers and pointers-to-const
147 * provide tighter, more correct semantics.
149 template<typename _Iterator
>
150 struct iterator_traits
;
152 #if __cplusplus >= 201103L
153 // _GLIBCXX_RESOLVE_LIB_DEFECTS
154 // 2408. SFINAE-friendly common_type/iterator_traits is missing in C++14
155 template<typename _Iterator
, typename
= __void_t
<>>
156 struct __iterator_traits
{ };
158 #if ! __cpp_lib_concepts
160 template<typename _Iterator
>
161 struct __iterator_traits
<_Iterator
,
162 __void_t
<typename
_Iterator::iterator_category
,
163 typename
_Iterator::value_type
,
164 typename
_Iterator::difference_type
,
165 typename
_Iterator::pointer
,
166 typename
_Iterator::reference
>>
168 typedef typename
_Iterator::iterator_category iterator_category
;
169 typedef typename
_Iterator::value_type value_type
;
170 typedef typename
_Iterator::difference_type difference_type
;
171 typedef typename
_Iterator::pointer pointer
;
172 typedef typename
_Iterator::reference reference
;
176 template<typename _Iterator
>
177 struct iterator_traits
178 : public __iterator_traits
<_Iterator
> { };
181 template<typename _Iterator
>
182 struct iterator_traits
184 typedef typename
_Iterator::iterator_category iterator_category
;
185 typedef typename
_Iterator::value_type value_type
;
186 typedef typename
_Iterator::difference_type difference_type
;
187 typedef typename
_Iterator::pointer pointer
;
188 typedef typename
_Iterator::reference reference
;
192 #if __cplusplus > 201703L
193 /// Partial specialization for object pointer types.
194 template<typename _Tp
>
195 #if __cpp_concepts >= 201907L
196 requires is_object_v
<_Tp
>
198 struct iterator_traits
<_Tp
*>
200 using iterator_concept
= contiguous_iterator_tag
;
201 using iterator_category
= random_access_iterator_tag
;
202 using value_type
= remove_cv_t
<_Tp
>;
203 using difference_type
= ptrdiff_t;
204 using pointer
= _Tp
*;
205 using reference
= _Tp
&;
208 /// Partial specialization for pointer types.
209 template<typename _Tp
>
210 struct iterator_traits
<_Tp
*>
212 typedef random_access_iterator_tag iterator_category
;
213 typedef _Tp value_type
;
214 typedef ptrdiff_t difference_type
;
215 typedef _Tp
* pointer
;
216 typedef _Tp
& reference
;
219 /// Partial specialization for const pointer types.
220 template<typename _Tp
>
221 struct iterator_traits
<const _Tp
*>
223 typedef random_access_iterator_tag iterator_category
;
224 typedef _Tp value_type
;
225 typedef ptrdiff_t difference_type
;
226 typedef const _Tp
* pointer
;
227 typedef const _Tp
& reference
;
232 * This function is not a part of the C++ standard but is syntactic
233 * sugar for internal library use only.
235 template<typename _Iter
>
236 inline _GLIBCXX_CONSTEXPR
237 typename iterator_traits
<_Iter
>::iterator_category
238 __iterator_category(const _Iter
&)
239 { return typename iterator_traits
<_Iter
>::iterator_category(); }
243 #if __cplusplus >= 201103L
244 template<typename _Iter
>
245 using __iterator_category_t
246 = typename iterator_traits
<_Iter
>::iterator_category
;
248 template<typename _InIter
>
249 using _RequireInputIter
=
250 __enable_if_t
<is_convertible
<__iterator_category_t
<_InIter
>,
251 input_iterator_tag
>::value
>;
253 template<typename _It
,
254 typename _Cat
= __iterator_category_t
<_It
>>
255 struct __is_random_access_iter
256 : is_base_of
<random_access_iterator_tag
, _Cat
>
258 typedef is_base_of
<random_access_iterator_tag
, _Cat
> _Base
;
259 enum { __value
= _Base::value
};
262 template<typename _It
, typename _Traits
= iterator_traits
<_It
>,
263 typename _Cat
= typename
_Traits::iterator_category
>
264 struct __is_random_access_iter
265 { enum { __value
= __is_base_of(random_access_iterator_tag
, _Cat
) }; };
268 _GLIBCXX_END_NAMESPACE_VERSION
271 #endif /* _STL_ITERATOR_BASE_TYPES_H */