1//===- iterator.h - Utilities for using and defining iterators --*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef LLVM_ADT_ITERATOR_H
10#define LLVM_ADT_ITERATOR_H
11
12#include "llvm/ADT/iterator_range.h"
13#include <algorithm>
14#include <cstddef>
15#include <iterator>
16#include <type_traits>
17#include <utility>
18
19namespace llvm {
20
21/// CRTP base class which implements the entire standard iterator facade
22/// in terms of a minimal subset of the interface.
23///
24/// Use this when it is reasonable to implement most of the iterator
25/// functionality in terms of a core subset. If you need special behavior or
26/// there are performance implications for this, you may want to override the
27/// relevant members instead.
28///
29/// Note, one abstraction that this does *not* provide is implementing
30/// subtraction in terms of addition by negating the difference. Negation isn't
31/// always information preserving, and I can see very reasonable iterator
32/// designs where this doesn't work well. It doesn't really force much added
33/// boilerplate anyways.
34///
35/// Another abstraction that this doesn't provide is implementing increment in
36/// terms of addition of one. These aren't equivalent for all iterator
37/// categories, and respecting that adds a lot of complexity for little gain.
38///
39/// Classes wishing to use `iterator_facade_base` should implement the following
40/// methods:
41///
42/// Forward Iterators:
43/// (All of the following methods)
44/// - DerivedT &operator=(const DerivedT &R);
45/// - bool operator==(const DerivedT &R) const;
46/// - const T &operator*() const;
47/// - T &operator*();
48/// - DerivedT &operator++();
49///
50/// Bidirectional Iterators:
51/// (All methods of forward iterators, plus the following)
52/// - DerivedT &operator--();
53///
54/// Random-access Iterators:
55/// (All methods of bidirectional iterators excluding the following)
56/// - DerivedT &operator++();
57/// - DerivedT &operator--();
58/// (and plus the following)
59/// - bool operator<(const DerivedT &RHS) const;
60/// - DifferenceTypeT operator-(const DerivedT &R) const;
61/// - DerivedT &operator+=(DifferenceTypeT N);
62/// - DerivedT &operator-=(DifferenceTypeT N);
63///
64template <typename DerivedT, typename IteratorCategoryT, typename T,
65 typename DifferenceTypeT = std::ptrdiff_t, typename PointerT = T *,
66 typename ReferenceT = T &>
67class iterator_facade_base
68 : public std::iterator<IteratorCategoryT, T, DifferenceTypeT, PointerT,
69 ReferenceT> {
70protected:
71 enum {
72 IsRandomAccess = std::is_base_of<std::random_access_iterator_tag,
73 IteratorCategoryT>::value,
74 IsBidirectional = std::is_base_of<std::bidirectional_iterator_tag,
75 IteratorCategoryT>::value,
76 };
77
78 /// A proxy object for computing a reference via indirecting a copy of an
79 /// iterator. This is used in APIs which need to produce a reference via
80 /// indirection but for which the iterator object might be a temporary. The
81 /// proxy preserves the iterator internally and exposes the indirected
82 /// reference via a conversion operator.
83 class ReferenceProxy {
84 friend iterator_facade_base;
85
86 DerivedT I;
87
88 ReferenceProxy(DerivedT I) : I(std::move(I)) {}
89
90 public:
91 operator ReferenceT() const { return *I; }
92 };
93
94public:
95 DerivedT operator+(DifferenceTypeT n) const {
96 static_assert(std::is_base_of<iterator_facade_base, DerivedT>::value,
97 "Must pass the derived type to this template!");
98 static_assert(
99 IsRandomAccess,
100 "The '+' operator is only defined for random access iterators.");
101 DerivedT tmp = *static_cast<const DerivedT *>(this);
102 tmp += n;
103 return tmp;
104 }
105 friend DerivedT operator+(DifferenceTypeT n, const DerivedT &i) {
106 static_assert(
107 IsRandomAccess,
108 "The '+' operator is only defined for random access iterators.");
109 return i + n;
110 }
111 DerivedT operator-(DifferenceTypeT n) const {
112 static_assert(
113 IsRandomAccess,
114 "The '-' operator is only defined for random access iterators.");
115 DerivedT tmp = *static_cast<const DerivedT *>(this);
116 tmp -= n;
117 return tmp;
118 }
119
120 DerivedT &operator++() {
121 static_assert(std::is_base_of<iterator_facade_base, DerivedT>::value,
122 "Must pass the derived type to this template!");
123 return static_cast<DerivedT *>(this)->operator+=(1);
124 }
125 DerivedT operator++(int) {
126 DerivedT tmp = *static_cast<DerivedT *>(this);
127 ++*static_cast<DerivedT *>(this);
128 return tmp;
129 }
130 DerivedT &operator--() {
131 static_assert(
132 IsBidirectional,
133 "The decrement operator is only defined for bidirectional iterators.");
134 return static_cast<DerivedT *>(this)->operator-=(1);
135 }
136 DerivedT operator--(int) {
137 static_assert(
138 IsBidirectional,
139 "The decrement operator is only defined for bidirectional iterators.");
140 DerivedT tmp = *static_cast<DerivedT *>(this);
141 --*static_cast<DerivedT *>(this);
142 return tmp;
143 }
144
145 bool operator!=(const DerivedT &RHS) const {
146 return !static_cast<const DerivedT *>(this)->operator==(RHS);
147 }
148
149 bool operator>(const DerivedT &RHS) const {
150 static_assert(
151 IsRandomAccess,
152 "Relational operators are only defined for random access iterators.");
153 return !static_cast<const DerivedT *>(this)->operator<(RHS) &&
154 !static_cast<const DerivedT *>(this)->operator==(RHS);
155 }
156 bool operator<=(const DerivedT &RHS) const {
157 static_assert(
158 IsRandomAccess,
159 "Relational operators are only defined for random access iterators.");
160 return !static_cast<const DerivedT *>(this)->operator>(RHS);
161 }
162 bool operator>=(const DerivedT &RHS) const {
163 static_assert(
164 IsRandomAccess,
165 "Relational operators are only defined for random access iterators.");
166 return !static_cast<const DerivedT *>(this)->operator<(RHS);
167 }
168
169 PointerT operator->() { return &static_cast<DerivedT *>(this)->operator*(); }
170 PointerT operator->() const {
171 return &static_cast<const DerivedT *>(this)->operator*();
172 }
173 ReferenceProxy operator[](DifferenceTypeT n) {
174 static_assert(IsRandomAccess,
175 "Subscripting is only defined for random access iterators.");
176 return ReferenceProxy(static_cast<DerivedT *>(this)->operator+(n));
177 }
178 ReferenceProxy operator[](DifferenceTypeT n) const {
179 static_assert(IsRandomAccess,
180 "Subscripting is only defined for random access iterators.");
181 return ReferenceProxy(static_cast<const DerivedT *>(this)->operator+(n));
182 }
183};
184
185/// CRTP base class for adapting an iterator to a different type.
186///
187/// This class can be used through CRTP to adapt one iterator into another.
188/// Typically this is done through providing in the derived class a custom \c
189/// operator* implementation. Other methods can be overridden as well.
190template <
191 typename DerivedT, typename WrappedIteratorT,
192 typename IteratorCategoryT =
193 typename std::iterator_traits<WrappedIteratorT>::iterator_category,
194 typename T = typename std::iterator_traits<WrappedIteratorT>::value_type,
195 typename DifferenceTypeT =
196 typename std::iterator_traits<WrappedIteratorT>::difference_type,
197 typename PointerT = typename std::conditional<
198 std::is_same<T, typename std::iterator_traits<
199 WrappedIteratorT>::value_type>::value,
200 typename std::iterator_traits<WrappedIteratorT>::pointer, T *>::type,
201 typename ReferenceT = typename std::conditional<
202 std::is_same<T, typename std::iterator_traits<
203 WrappedIteratorT>::value_type>::value,
204 typename std::iterator_traits<WrappedIteratorT>::reference, T &>::type>
205class iterator_adaptor_base
206 : public iterator_facade_base<DerivedT, IteratorCategoryT, T,
207 DifferenceTypeT, PointerT, ReferenceT> {
208 using BaseT = typename iterator_adaptor_base::iterator_facade_base;
209
210protected:
211 WrappedIteratorT I;
212
213 iterator_adaptor_base() = default;
214
215 explicit iterator_adaptor_base(WrappedIteratorT u) : I(std::move(u)) {
216 static_assert(std::is_base_of<iterator_adaptor_base, DerivedT>::value,
217 "Must pass the derived type to this template!");
218 }
219
220 const WrappedIteratorT &wrapped() const { return I; }
221
222public:
223 using difference_type = DifferenceTypeT;
224
225 DerivedT &operator+=(difference_type n) {
226 static_assert(
227 BaseT::IsRandomAccess,
228 "The '+=' operator is only defined for random access iterators.");
229 I += n;
230 return *static_cast<DerivedT *>(this);
231 }
232 DerivedT &operator-=(difference_type n) {
233 static_assert(
234 BaseT::IsRandomAccess,
235 "The '-=' operator is only defined for random access iterators.");
236 I -= n;
237 return *static_cast<DerivedT *>(this);
238 }
239 using BaseT::operator-;
240 difference_type operator-(const DerivedT &RHS) const {
241 static_assert(
242 BaseT::IsRandomAccess,
243 "The '-' operator is only defined for random access iterators.");
244 return I - RHS.I;
245 }
246
247 // We have to explicitly provide ++ and -- rather than letting the facade
248 // forward to += because WrappedIteratorT might not support +=.
249 using BaseT::operator++;
250 DerivedT &operator++() {
251 ++I;
252 return *static_cast<DerivedT *>(this);
253 }
254 using BaseT::operator--;
255 DerivedT &operator--() {
256 static_assert(
257 BaseT::IsBidirectional,
258 "The decrement operator is only defined for bidirectional iterators.");
259 --I;
260 return *static_cast<DerivedT *>(this);
261 }
262
263 bool operator==(const DerivedT &RHS) const { return I == RHS.I; }
264 bool operator<(const DerivedT &RHS) const {
265 static_assert(
266 BaseT::IsRandomAccess,
267 "Relational operators are only defined for random access iterators.");
268 return I < RHS.I;
269 }
270
271 ReferenceT operator*() const { return *I; }
272};
273
274/// An iterator type that allows iterating over the pointees via some
275/// other iterator.
276///
277/// The typical usage of this is to expose a type that iterates over Ts, but
278/// which is implemented with some iterator over T*s:
279///
280/// \code
281/// using iterator = pointee_iterator<SmallVectorImpl<T *>::iterator>;
282/// \endcode
283template <typename WrappedIteratorT,
284 typename T = typename std::remove_reference<
285 decltype(**std::declval<WrappedIteratorT>())>::type>
286struct pointee_iterator
287 : iterator_adaptor_base<
288 pointee_iterator<WrappedIteratorT, T>, WrappedIteratorT,
289 typename std::iterator_traits<WrappedIteratorT>::iterator_category,
290 T> {
291 pointee_iterator() = default;
292 template <typename U>
293 pointee_iterator(U &&u)
294 : pointee_iterator::iterator_adaptor_base(std::forward<U &&>(u)) {}
295
296 T &operator*() const { return **this->I; }
297};
298
299template <typename RangeT, typename WrappedIteratorT =
300 decltype(std::begin(std::declval<RangeT>()))>
301iterator_range<pointee_iterator<WrappedIteratorT>>
302make_pointee_range(RangeT &&Range) {
303 using PointeeIteratorT = pointee_iterator<WrappedIteratorT>;
304 return make_range(PointeeIteratorT(std::begin(std::forward<RangeT>(Range))),
305 PointeeIteratorT(std::end(std::forward<RangeT>(Range))));
306}
307
308template <typename WrappedIteratorT,
309 typename T = decltype(&*std::declval<WrappedIteratorT>())>
310class pointer_iterator
311 : public iterator_adaptor_base<
312 pointer_iterator<WrappedIteratorT, T>, WrappedIteratorT,
313 typename std::iterator_traits<WrappedIteratorT>::iterator_category,
314 T> {
315 mutable T Ptr;
316
317public:
318 pointer_iterator() = default;
319
320 explicit pointer_iterator(WrappedIteratorT u)
321 : pointer_iterator::iterator_adaptor_base(std::move(u)) {}
322
323 T &operator*() { return Ptr = &*this->I; }
324 const T &operator*() const { return Ptr = &*this->I; }
325};
326
327template <typename RangeT, typename WrappedIteratorT =
328 decltype(std::begin(std::declval<RangeT>()))>
329iterator_range<pointer_iterator<WrappedIteratorT>>
330make_pointer_range(RangeT &&Range) {
331 using PointerIteratorT = pointer_iterator<WrappedIteratorT>;
332 return make_range(PointerIteratorT(std::begin(std::forward<RangeT>(Range))),
333 PointerIteratorT(std::end(std::forward<RangeT>(Range))));
334}
335
336// Wrapper iterator over iterator ItType, adding DataRef to the type of ItType,
337// to create NodeRef = std::pair<InnerTypeOfItType, DataRef>.
338template <typename ItType, typename NodeRef, typename DataRef>
339class WrappedPairNodeDataIterator
340 : public iterator_adaptor_base<
341 WrappedPairNodeDataIterator<ItType, NodeRef, DataRef>, ItType,
342 typename std::iterator_traits<ItType>::iterator_category, NodeRef,
343 std::ptrdiff_t, NodeRef *, NodeRef &> {
344 using BaseT = iterator_adaptor_base<
345 WrappedPairNodeDataIterator, ItType,
346 typename std::iterator_traits<ItType>::iterator_category, NodeRef,
347 std::ptrdiff_t, NodeRef *, NodeRef &>;
348
349 const DataRef DR;
350 mutable NodeRef NR;
351
352public:
353 WrappedPairNodeDataIterator(ItType Begin, const DataRef DR)
354 : BaseT(Begin), DR(DR) {
355 NR.first = DR;
356 }
357
358 NodeRef &operator*() const {
359 NR.second = *this->I;
360 return NR;
361 }
362};
363
364} // end namespace llvm
365
366#endif // LLVM_ADT_ITERATOR_H
367