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iterator.h
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1 //===- iterator.h - Utilities for using and defining iterators --*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef LLVM_ADT_ITERATOR_H
11 #define LLVM_ADT_ITERATOR_H
12 
14 #include <algorithm>
15 #include <cstddef>
16 #include <iterator>
17 #include <type_traits>
18 #include <utility>
19 
20 namespace llvm {
21 
22 /// \brief CRTP base class which implements the entire standard iterator facade
23 /// in terms of a minimal subset of the interface.
24 ///
25 /// Use this when it is reasonable to implement most of the iterator
26 /// functionality in terms of a core subset. If you need special behavior or
27 /// there are performance implications for this, you may want to override the
28 /// relevant members instead.
29 ///
30 /// Note, one abstraction that this does *not* provide is implementing
31 /// subtraction in terms of addition by negating the difference. Negation isn't
32 /// always information preserving, and I can see very reasonable iterator
33 /// designs where this doesn't work well. It doesn't really force much added
34 /// boilerplate anyways.
35 ///
36 /// Another abstraction that this doesn't provide is implementing increment in
37 /// terms of addition of one. These aren't equivalent for all iterator
38 /// categories, and respecting that adds a lot of complexity for little gain.
39 ///
40 /// Classes wishing to use `iterator_facade_base` should implement the following
41 /// methods:
42 ///
43 /// Forward Iterators:
44 /// (All of the following methods)
45 /// - DerivedT &operator=(const DerivedT &R);
46 /// - bool operator==(const DerivedT &R) const;
47 /// - const T &operator*() const;
48 /// - T &operator*();
49 /// - DerivedT &operator++();
50 ///
51 /// Bidirectional Iterators:
52 /// (All methods of forward iterators, plus the following)
53 /// - DerivedT &operator--();
54 ///
55 /// Random-access Iterators:
56 /// (All methods of bidirectional iterators excluding the following)
57 /// - DerivedT &operator++();
58 /// - DerivedT &operator--();
59 /// (and plus the following)
60 /// - bool operator<(const DerivedT &RHS) const;
61 /// - DifferenceTypeT operator-(const DerivedT &R) const;
62 /// - DerivedT &operator+=(DifferenceTypeT N);
63 /// - DerivedT &operator-=(DifferenceTypeT N);
64 ///
65 template <typename DerivedT, typename IteratorCategoryT, typename T,
66  typename DifferenceTypeT = std::ptrdiff_t, typename PointerT = T *,
67  typename ReferenceT = T &>
69  : public std::iterator<IteratorCategoryT, T, DifferenceTypeT, PointerT,
70  ReferenceT> {
71 protected:
72  enum {
73  IsRandomAccess = std::is_base_of<std::random_access_iterator_tag,
74  IteratorCategoryT>::value,
75  IsBidirectional = std::is_base_of<std::bidirectional_iterator_tag,
76  IteratorCategoryT>::value,
77  };
78 
79  /// A proxy object for computing a reference via indirecting a copy of an
80  /// iterator. This is used in APIs which need to produce a reference via
81  /// indirection but for which the iterator object might be a temporary. The
82  /// proxy preserves the iterator internally and exposes the indirected
83  /// reference via a conversion operator.
85  friend iterator_facade_base;
86 
87  DerivedT I;
88 
89  ReferenceProxy(DerivedT I) : I(std::move(I)) {}
90 
91  public:
92  operator ReferenceT() const { return *I; }
93  };
94 
95 public:
96  DerivedT operator+(DifferenceTypeT n) const {
97  static_assert(std::is_base_of<iterator_facade_base, DerivedT>::value,
98  "Must pass the derived type to this template!");
99  static_assert(
101  "The '+' operator is only defined for random access iterators.");
102  DerivedT tmp = *static_cast<const DerivedT *>(this);
103  tmp += n;
104  return tmp;
105  }
106  friend DerivedT operator+(DifferenceTypeT n, const DerivedT &i) {
107  static_assert(
109  "The '+' operator is only defined for random access iterators.");
110  return i + n;
111  }
112  DerivedT operator-(DifferenceTypeT n) const {
113  static_assert(
115  "The '-' operator is only defined for random access iterators.");
116  DerivedT tmp = *static_cast<const DerivedT *>(this);
117  tmp -= n;
118  return tmp;
119  }
120 
121  DerivedT &operator++() {
122  static_assert(std::is_base_of<iterator_facade_base, DerivedT>::value,
123  "Must pass the derived type to this template!");
124  return static_cast<DerivedT *>(this)->operator+=(1);
125  }
126  DerivedT operator++(int) {
127  DerivedT tmp = *static_cast<DerivedT *>(this);
128  ++*static_cast<DerivedT *>(this);
129  return tmp;
130  }
131  DerivedT &operator--() {
132  static_assert(
134  "The decrement operator is only defined for bidirectional iterators.");
135  return static_cast<DerivedT *>(this)->operator-=(1);
136  }
137  DerivedT operator--(int) {
138  static_assert(
140  "The decrement operator is only defined for bidirectional iterators.");
141  DerivedT tmp = *static_cast<DerivedT *>(this);
142  --*static_cast<DerivedT *>(this);
143  return tmp;
144  }
145 
146  bool operator!=(const DerivedT &RHS) const {
147  return !static_cast<const DerivedT *>(this)->operator==(RHS);
148  }
149 
150  bool operator>(const DerivedT &RHS) const {
151  static_assert(
153  "Relational operators are only defined for random access iterators.");
154  return !static_cast<const DerivedT *>(this)->operator<(RHS) &&
155  !static_cast<const DerivedT *>(this)->operator==(RHS);
156  }
157  bool operator<=(const DerivedT &RHS) const {
158  static_assert(
160  "Relational operators are only defined for random access iterators.");
161  return !static_cast<const DerivedT *>(this)->operator>(RHS);
162  }
163  bool operator>=(const DerivedT &RHS) const {
164  static_assert(
166  "Relational operators are only defined for random access iterators.");
167  return !static_cast<const DerivedT *>(this)->operator<(RHS);
168  }
169 
170  PointerT operator->() { return &static_cast<DerivedT *>(this)->operator*(); }
171  PointerT operator->() const {
172  return &static_cast<const DerivedT *>(this)->operator*();
173  }
174  ReferenceProxy operator[](DifferenceTypeT n) {
175  static_assert(IsRandomAccess,
176  "Subscripting is only defined for random access iterators.");
177  return ReferenceProxy(static_cast<DerivedT *>(this)->operator+(n));
178  }
179  ReferenceProxy operator[](DifferenceTypeT n) const {
180  static_assert(IsRandomAccess,
181  "Subscripting is only defined for random access iterators.");
182  return ReferenceProxy(static_cast<const DerivedT *>(this)->operator+(n));
183  }
184 };
185 
186 /// \brief CRTP base class for adapting an iterator to a different type.
187 ///
188 /// This class can be used through CRTP to adapt one iterator into another.
189 /// Typically this is done through providing in the derived class a custom \c
190 /// operator* implementation. Other methods can be overridden as well.
191 template <
192  typename DerivedT, typename WrappedIteratorT,
193  typename IteratorCategoryT =
194  typename std::iterator_traits<WrappedIteratorT>::iterator_category,
195  typename T = typename std::iterator_traits<WrappedIteratorT>::value_type,
196  typename DifferenceTypeT =
197  typename std::iterator_traits<WrappedIteratorT>::difference_type,
198  typename PointerT = typename std::conditional<
199  std::is_same<T, typename std::iterator_traits<
200  WrappedIteratorT>::value_type>::value,
201  typename std::iterator_traits<WrappedIteratorT>::pointer, T *>::type,
202  typename ReferenceT = typename std::conditional<
203  std::is_same<T, typename std::iterator_traits<
204  WrappedIteratorT>::value_type>::value,
205  typename std::iterator_traits<WrappedIteratorT>::reference, T &>::type,
206  // Don't provide these, they are mostly to act as aliases below.
207  typename WrappedTraitsT = std::iterator_traits<WrappedIteratorT>>
209  : public iterator_facade_base<DerivedT, IteratorCategoryT, T,
210  DifferenceTypeT, PointerT, ReferenceT> {
211  using BaseT = typename iterator_adaptor_base::iterator_facade_base;
212 
213 protected:
214  WrappedIteratorT I;
215 
216  iterator_adaptor_base() = default;
217 
218  explicit iterator_adaptor_base(WrappedIteratorT u) : I(std::move(u)) {
219  static_assert(std::is_base_of<iterator_adaptor_base, DerivedT>::value,
220  "Must pass the derived type to this template!");
221  }
222 
223  const WrappedIteratorT &wrapped() const { return I; }
224 
225 public:
226  using difference_type = DifferenceTypeT;
227 
229  static_assert(
230  BaseT::IsRandomAccess,
231  "The '+=' operator is only defined for random access iterators.");
232  I += n;
233  return *static_cast<DerivedT *>(this);
234  }
236  static_assert(
237  BaseT::IsRandomAccess,
238  "The '-=' operator is only defined for random access iterators.");
239  I -= n;
240  return *static_cast<DerivedT *>(this);
241  }
242  using BaseT::operator-;
243  difference_type operator-(const DerivedT &RHS) const {
244  static_assert(
245  BaseT::IsRandomAccess,
246  "The '-' operator is only defined for random access iterators.");
247  return I - RHS.I;
248  }
249 
250  // We have to explicitly provide ++ and -- rather than letting the facade
251  // forward to += because WrappedIteratorT might not support +=.
252  using BaseT::operator++;
253  DerivedT &operator++() {
254  ++I;
255  return *static_cast<DerivedT *>(this);
256  }
257  using BaseT::operator--;
258  DerivedT &operator--() {
259  static_assert(
260  BaseT::IsBidirectional,
261  "The decrement operator is only defined for bidirectional iterators.");
262  --I;
263  return *static_cast<DerivedT *>(this);
264  }
265 
266  bool operator==(const DerivedT &RHS) const { return I == RHS.I; }
267  bool operator<(const DerivedT &RHS) const {
268  static_assert(
269  BaseT::IsRandomAccess,
270  "Relational operators are only defined for random access iterators.");
271  return I < RHS.I;
272  }
273 
274  ReferenceT operator*() const { return *I; }
275 };
276 
277 /// \brief An iterator type that allows iterating over the pointees via some
278 /// other iterator.
279 ///
280 /// The typical usage of this is to expose a type that iterates over Ts, but
281 /// which is implemented with some iterator over T*s:
282 ///
283 /// \code
284 /// using iterator = pointee_iterator<SmallVectorImpl<T *>::iterator>;
285 /// \endcode
286 template <typename WrappedIteratorT,
287  typename T = typename std::remove_reference<
288  decltype(**std::declval<WrappedIteratorT>())>::type>
291  pointee_iterator<WrappedIteratorT>, WrappedIteratorT,
292  typename std::iterator_traits<WrappedIteratorT>::iterator_category,
293  T> {
294  pointee_iterator() = default;
295  template <typename U>
297  : pointee_iterator::iterator_adaptor_base(std::forward<U &&>(u)) {}
298 
299  T &operator*() const { return **this->I; }
300 };
301 
302 template <typename RangeT, typename WrappedIteratorT =
303  decltype(std::begin(std::declval<RangeT>()))>
305 make_pointee_range(RangeT &&Range) {
306  using PointeeIteratorT = pointee_iterator<WrappedIteratorT>;
307  return make_range(PointeeIteratorT(std::begin(std::forward<RangeT>(Range))),
308  PointeeIteratorT(std::end(std::forward<RangeT>(Range))));
309 }
310 
311 template <typename WrappedIteratorT,
312  typename T = decltype(&*std::declval<WrappedIteratorT>())>
314  : public iterator_adaptor_base<pointer_iterator<WrappedIteratorT>,
315  WrappedIteratorT, T> {
316  mutable T Ptr;
317 
318 public:
319  pointer_iterator() = default;
320 
321  explicit pointer_iterator(WrappedIteratorT u)
323 
324  T &operator*() { return Ptr = &*this->I; }
325  const T &operator*() const { return Ptr = &*this->I; }
326 };
327 
328 template <typename RangeT, typename WrappedIteratorT =
329  decltype(std::begin(std::declval<RangeT>()))>
331 make_pointer_range(RangeT &&Range) {
332  using PointerIteratorT = pointer_iterator<WrappedIteratorT>;
333  return make_range(PointerIteratorT(std::begin(std::forward<RangeT>(Range))),
334  PointerIteratorT(std::end(std::forward<RangeT>(Range))));
335 }
336 
337 } // end namespace llvm
338 
339 #endif // LLVM_ADT_ITERATOR_H
WrappedIteratorT I
Definition: iterator.h:214
const_iterator end(StringRef path)
Get end iterator over path.
Definition: Path.cpp:244
DerivedT operator-(DifferenceTypeT n) const
Definition: iterator.h:112
iterator_adaptor_base(WrappedIteratorT u)
Definition: iterator.h:218
const_iterator begin(StringRef path, Style style=Style::native)
Get begin iterator over path.
Definition: Path.cpp:235
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
bool operator!=(const DerivedT &RHS) const
Definition: iterator.h:146
bool operator>=(const DerivedT &RHS) const
Definition: iterator.h:163
This provides a very simple, boring adaptor for a begin and end iterator into a range type...
bool operator<=(const DerivedT &RHS) const
Definition: iterator.h:157
bool operator<(const DerivedT &RHS) const
Definition: iterator.h:267
A proxy object for computing a reference via indirecting a copy of an iterator.
Definition: iterator.h:84
Definition: BitVector.h:920
ReferenceT operator*() const
Definition: iterator.h:274
DerivedT & operator--()
Definition: iterator.h:131
DerivedT & operator+=(difference_type n)
Definition: iterator.h:228
#define T
CRTP base class which implements the entire standard iterator facade in terms of a minimal subset of ...
Definition: iterator.h:68
const WrappedIteratorT & wrapped() const
Definition: iterator.h:223
difference_type operator-(const DerivedT &RHS) const
Definition: iterator.h:243
CRTP base class for adapting an iterator to a different type.
Definition: iterator.h:208
ReferenceProxy operator[](DifferenceTypeT n)
Definition: iterator.h:174
friend DerivedT operator+(DifferenceTypeT n, const DerivedT &i)
Definition: iterator.h:106
DerivedT operator+(DifferenceTypeT n) const
Definition: iterator.h:96
iterator_range< T > make_range(T x, T y)
Convenience function for iterating over sub-ranges.
ReferenceProxy operator[](DifferenceTypeT n) const
Definition: iterator.h:179
DerivedT & operator++()
Definition: iterator.h:121
PointerT operator->() const
Definition: iterator.h:171
An iterator type that allows iterating over the pointees via some other iterator. ...
Definition: iterator.h:289
T & operator*() const
Definition: iterator.h:299
A range adaptor for a pair of iterators.
pointer_iterator(WrappedIteratorT u)
Definition: iterator.h:321
bool operator==(const DerivedT &RHS) const
Definition: iterator.h:266
#define I(x, y, z)
Definition: MD5.cpp:58
iterator_range< pointee_iterator< WrappedIteratorT > > make_pointee_range(RangeT &&Range)
Definition: iterator.h:305
const T & operator*() const
Definition: iterator.h:325
DerivedT operator--(int)
Definition: iterator.h:137
DerivedT operator++(int)
Definition: iterator.h:126
DerivedT & operator-=(difference_type n)
Definition: iterator.h:235
bool operator>(const DerivedT &RHS) const
Definition: iterator.h:150
iterator_range< pointer_iterator< WrappedIteratorT > > make_pointer_range(RangeT &&Range)
Definition: iterator.h:331