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 //===----------------------------------------------------------------------===//
10 #ifndef LLVM_ADT_ITERATOR_H
11 #define LLVM_ADT_ITERATOR_H
13 #include <cstddef>
14 #include <iterator>
16 namespace llvm {
18 /// \brief CRTP base class which implements the entire standard iterator facade
19 /// in terms of a minimal subset of the interface.
20 ///
21 /// Use this when it is reasonable to implement most of the iterator
22 /// functionality in terms of a core subset. If you need special behavior or
23 /// there are performance implications for this, you may want to override the
24 /// relevant members instead.
25 ///
26 /// Note, one abstraction that this does *not* provide is implementing
27 /// subtraction in terms of addition by negating the difference. Negation isn't
28 /// always information preserving, and I can see very reasonable iterator
29 /// designs where this doesn't work well. It doesn't really force much added
30 /// boilerplate anyways.
31 ///
32 /// Another abstraction that this doesn't provide is implementing increment in
33 /// terms of addition of one. These aren't equivalent for all iterator
34 /// categories, and respecting that adds a lot of complexity for little gain.
35 template <typename DerivedT, typename IteratorCategoryT, typename T,
36 typename DifferenceTypeT = std::ptrdiff_t, typename PointerT = T *,
37 typename ReferenceT = T &>
38 class iterator_facade_base
39 : public std::iterator<IteratorCategoryT, T, DifferenceTypeT, PointerT,
40 ReferenceT> {
41 protected:
42 enum {
43 IsRandomAccess =
44 std::is_base_of<std::random_access_iterator_tag, IteratorCategoryT>::value,
45 IsBidirectional =
46 std::is_base_of<std::bidirectional_iterator_tag, IteratorCategoryT>::value,
47 };
49 public:
50 DerivedT operator+(DifferenceTypeT n) const {
51 static_assert(
52 IsRandomAccess,
53 "The '+' operator is only defined for random access iterators.");
54 DerivedT tmp = *static_cast<const DerivedT *>(this);
55 tmp += n;
56 return tmp;
57 }
58 friend DerivedT operator+(DifferenceTypeT n, const DerivedT &i) {
59 static_assert(
60 IsRandomAccess,
61 "The '+' operator is only defined for random access iterators.");
62 return i + n;
63 }
64 DerivedT operator-(DifferenceTypeT n) const {
65 static_assert(
66 IsRandomAccess,
67 "The '-' operator is only defined for random access iterators.");
68 DerivedT tmp = *static_cast<const DerivedT *>(this);
69 tmp -= n;
70 return tmp;
71 }
73 DerivedT &operator++() {
74 return static_cast<DerivedT *>(this)->operator+=(1);
75 }
76 DerivedT operator++(int) {
77 DerivedT tmp = *static_cast<DerivedT *>(this);
78 ++*static_cast<DerivedT *>(this);
79 return tmp;
80 }
81 DerivedT &operator--() {
82 static_assert(
83 IsBidirectional,
84 "The decrement operator is only defined for bidirectional iterators.");
85 return static_cast<DerivedT *>(this)->operator-=(1);
86 }
87 DerivedT operator--(int) {
88 static_assert(
89 IsBidirectional,
90 "The decrement operator is only defined for bidirectional iterators.");
91 DerivedT tmp = *static_cast<DerivedT *>(this);
92 --*static_cast<DerivedT *>(this);
93 return tmp;
94 }
96 bool operator!=(const DerivedT &RHS) const {
97 return !static_cast<const DerivedT *>(this)->operator==(RHS);
98 }
100 bool operator>(const DerivedT &RHS) const {
101 static_assert(
102 IsRandomAccess,
103 "Relational operators are only defined for random access iterators.");
104 return !static_cast<const DerivedT *>(this)->operator<(RHS) &&
105 !static_cast<const DerivedT *>(this)->operator==(RHS);
106 }
107 bool operator<=(const DerivedT &RHS) const {
108 static_assert(
109 IsRandomAccess,
110 "Relational operators are only defined for random access iterators.");
111 return !static_cast<const DerivedT *>(this)->operator>(RHS);
112 }
113 bool operator>=(const DerivedT &RHS) const {
114 static_assert(
115 IsRandomAccess,
116 "Relational operators are only defined for random access iterators.");
117 return !static_cast<const DerivedT *>(this)->operator<(RHS);
118 }
120 PointerT operator->() const {
121 return &static_cast<const DerivedT *>(this)->operator*();
122 }
123 ReferenceT operator[](DifferenceTypeT n) const {
124 static_assert(IsRandomAccess,
125 "Subscripting is only defined for random access iterators.");
126 return *static_cast<const DerivedT *>(this)->operator+(n);
127 }
128 };
130 /// \brief CRTP base class for adapting an iterator to a different type.
131 ///
132 /// This class can be used through CRTP to adapt one iterator into another.
133 /// Typically this is done through providing in the derived class a custom \c
134 /// operator* implementation. Other methods can be overridden as well.
135 template <
136 typename DerivedT, typename WrappedIteratorT,
137 typename IteratorCategoryT =
138 typename std::iterator_traits<WrappedIteratorT>::iterator_category,
139 typename T = typename std::iterator_traits<WrappedIteratorT>::value_type,
140 typename DifferenceTypeT =
141 typename std::iterator_traits<WrappedIteratorT>::difference_type,
142 typename PointerT = T *, typename ReferenceT = T &,
143 // Don't provide these, they are mostly to act as aliases below.
144 typename WrappedTraitsT = std::iterator_traits<WrappedIteratorT>>
145 class iterator_adaptor_base
146 : public iterator_facade_base<DerivedT, IteratorCategoryT, T,
147 DifferenceTypeT, PointerT, ReferenceT> {
148 typedef typename iterator_adaptor_base::iterator_facade_base BaseT;
150 protected:
151 WrappedIteratorT I;
153 iterator_adaptor_base() {}
155 template <typename U>
156 explicit iterator_adaptor_base(
157 U &&u,
158 typename std::enable_if<
159 !std::is_base_of<typename std::remove_cv<
160 typename std::remove_reference<U>::type>::type,
161 DerivedT>::value,
162 int>::type = 0)
163 : I(std::forward<U &&>(u)) {}
165 public:
166 typedef DifferenceTypeT difference_type;
168 DerivedT &operator+=(difference_type n) {
169 static_assert(
170 BaseT::IsRandomAccess,
171 "The '+=' operator is only defined for random access iterators.");
172 I += n;
173 return *static_cast<DerivedT *>(this);
174 }
175 DerivedT &operator-=(difference_type n) {
176 static_assert(
177 BaseT::IsRandomAccess,
178 "The '-=' operator is only defined for random access iterators.");
179 I -= n;
180 return *static_cast<DerivedT *>(this);
181 }
182 using BaseT::operator-;
183 difference_type operator-(const DerivedT &RHS) const {
184 static_assert(
185 BaseT::IsRandomAccess,
186 "The '-' operator is only defined for random access iterators.");
187 return I - RHS.I;
188 }
190 // We have to explicitly provide ++ and -- rather than letting the facade
191 // forward to += because WrappedIteratorT might not support +=.
192 using BaseT::operator++;
193 DerivedT &operator++() {
194 ++I;
195 return *static_cast<DerivedT *>(this);
196 }
197 using BaseT::operator--;
198 DerivedT &operator--() {
199 static_assert(
200 BaseT::IsBidirectional,
201 "The decrement operator is only defined for bidirectional iterators.");
202 --I;
203 return *static_cast<DerivedT *>(this);
204 }
206 bool operator==(const DerivedT &RHS) const { return I == RHS.I; }
207 bool operator<(const DerivedT &RHS) const {
208 static_assert(
209 BaseT::IsRandomAccess,
210 "Relational operators are only defined for random access iterators.");
211 return I < RHS.I;
212 }
214 ReferenceT operator*() const { return *I; }
215 };
217 /// \brief An iterator type that allows iterating over the pointees via some
218 /// other iterator.
219 ///
220 /// The typical usage of this is to expose a type that iterates over Ts, but
221 /// which is implemented with some iterator over T*s:
222 ///
223 /// \code
224 /// typedef pointee_iterator<SmallVectorImpl<T *>::iterator> iterator;
225 /// \endcode
226 template <typename WrappedIteratorT,
227 typename T = typename std::remove_reference<
228 decltype(**std::declval<WrappedIteratorT>())>::type>
229 struct pointee_iterator
230 : iterator_adaptor_base<
231 pointee_iterator<WrappedIteratorT>, WrappedIteratorT,
232 typename std::iterator_traits<WrappedIteratorT>::iterator_category,
233 T> {
234 pointee_iterator() {}
235 template <typename U>
236 pointee_iterator(U &&u)
237 : pointee_iterator::iterator_adaptor_base(std::forward<U &&>(u)) {}
239 T &operator*() const { return **this->I; }
240 };
242 }
244 #endif