libstdc++
stl_iterator_base_types.h
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1 // Types used in iterator implementation -*- C++ -*-
2 
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4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
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16 // Under Section 7 of GPL version 3, you are granted additional
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24 
25 /*
26  *
27  * Copyright (c) 1994
28  * Hewlett-Packard Company
29  *
30  * Permission to use, copy, modify, distribute and sell this software
31  * and its documentation for any purpose is hereby granted without fee,
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33  * that both that copyright notice and this permission notice appear
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36  * purpose. It is provided "as is" without express or implied warranty.
37  *
38  *
39  * Copyright (c) 1996-1998
40  * Silicon Graphics Computer Systems, Inc.
41  *
42  * Permission to use, copy, modify, distribute and sell this software
43  * and its documentation for any purpose is hereby granted without fee,
44  * provided that the above copyright notice appear in all copies and
45  * that both that copyright notice and this permission notice appear
46  * in supporting documentation. Silicon Graphics makes no
47  * representations about the suitability of this software for any
48  * purpose. It is provided "as is" without express or implied warranty.
49  */
50 
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}
54  *
55  * This file contains all of the general iterator-related utility types,
56  * such as iterator_traits and struct iterator.
57  */
58 
59 #ifndef _STL_ITERATOR_BASE_TYPES_H
60 #define _STL_ITERATOR_BASE_TYPES_H 1
61 
62 #pragma GCC system_header
63 
64 #include <bits/c++config.h>
65 
66 #if __cplusplus >= 201103L
67 # include <type_traits> // For __void_t, is_convertible
68 #endif
69 
70 #if __cplusplus > 201703L && __cpp_concepts >= 201907L
71 # include <bits/iterator_concepts.h>
72 #endif
73 
74 namespace std _GLIBCXX_VISIBILITY(default)
75 {
76 _GLIBCXX_BEGIN_NAMESPACE_VERSION
77 
78  /**
79  * @defgroup iterators Iterators
80  * Abstractions for uniform iterating through various underlying types.
81  */
82  ///@{
83 
84  /**
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.
90  */
91  ///@{
92  /// Marking input iterators.
93  struct input_iterator_tag { };
94 
95  /// Marking output iterators.
96  struct output_iterator_tag { };
97 
98  /// Forward iterators support a superset of input iterator operations.
100 
101  /// Bidirectional iterators support a superset of forward iterator
102  /// operations.
104 
105  /// Random-access iterators support a superset of bidirectional
106  /// iterator operations.
108 
109 #if __cplusplus > 201703L
110  /// Contiguous iterators point to objects stored contiguously in memory.
111  struct contiguous_iterator_tag : public random_access_iterator_tag { };
112 #endif
113  ///@}
114 
115  /**
116  * @brief Common %iterator class.
117  *
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.
121  *
122  * In particular, there are no default implementations of requirements
123  * such as @c operator++ and the like. (How could there be?)
124  */
125  template<typename _Category, typename _Tp, typename _Distance = ptrdiff_t,
126  typename _Pointer = _Tp*, typename _Reference = _Tp&>
127  struct iterator
128  {
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;
139  };
140 
141  /**
142  * @brief Traits class for iterators.
143  *
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.
148  */
149  template<typename _Iterator>
150  struct iterator_traits;
151 
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 { };
157 
158 #if ! __cpp_lib_concepts
159 
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>>
167  {
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;
173  };
174 #endif // ! concepts
175 
176  template<typename _Iterator>
178  : public __iterator_traits<_Iterator> { };
179 
180 #else // ! C++11
181  template<typename _Iterator>
182  struct iterator_traits
183  {
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;
189  };
190 #endif // C++11
191 
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>
197 #endif
198  struct iterator_traits<_Tp*>
199  {
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&;
206  };
207 #else
208  /// Partial specialization for pointer types.
209  template<typename _Tp>
210  struct iterator_traits<_Tp*>
211  {
213  typedef _Tp value_type;
214  typedef ptrdiff_t difference_type;
215  typedef _Tp* pointer;
216  typedef _Tp& reference;
217  };
218 
219  /// Partial specialization for const pointer types.
220  template<typename _Tp>
221  struct iterator_traits<const _Tp*>
222  {
224  typedef _Tp value_type;
225  typedef ptrdiff_t difference_type;
226  typedef const _Tp* pointer;
227  typedef const _Tp& reference;
228  };
229 #endif
230 
231  /**
232  * This function is not a part of the C++ standard but is syntactic
233  * sugar for internal library use only.
234  */
235  template<typename _Iter>
236  inline _GLIBCXX_CONSTEXPR
238  __iterator_category(const _Iter&)
239  { return typename iterator_traits<_Iter>::iterator_category(); }
240 
241  ///@}
242 
243 #if __cplusplus >= 201103L
244  template<typename _Iter>
245  using __iterator_category_t
246  = typename iterator_traits<_Iter>::iterator_category;
247 
248  template<typename _InIter>
249  using _RequireInputIter =
250  __enable_if_t<is_convertible<__iterator_category_t<_InIter>,
251  input_iterator_tag>::value>;
252 
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>
257  {
258  typedef is_base_of<random_access_iterator_tag, _Cat> _Base;
259  enum { __value = _Base::value };
260  };
261 #else
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) }; };
266 #endif
267 
268 _GLIBCXX_END_NAMESPACE_VERSION
269 } // namespace
270 
271 #endif /* _STL_ITERATOR_BASE_TYPES_H */
constexpr iterator_traits< _Iter >::iterator_category __iterator_category(const _Iter &)
ISO C++ entities toplevel namespace is std.
Traits class for iterators.
Marking input iterators.
Marking output iterators.
Forward iterators support a superset of input iterator operations.
Bidirectional iterators support a superset of forward iterator operations.
Random-access iterators support a superset of bidirectional iterator operations.
Common iterator class.
_Category iterator_category
One of the tag types.
_Pointer pointer
This type represents a pointer-to-value_type.
_Distance difference_type
Distance between iterators is represented as this type.
_Reference reference
This type represents a reference-to-value_type.
_Tp value_type
The type "pointed to" by the iterator.