LLVM  3.7.0
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 
13 #include <cstddef>
14 #include <iterator>
15 
16 namespace llvm {
17 
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 &>
39  : public std::iterator<IteratorCategoryT, T, DifferenceTypeT, PointerT,
40  ReferenceT> {
41 protected:
42  enum {
44  std::is_base_of<std::random_access_iterator_tag, IteratorCategoryT>::value,
46  std::is_base_of<std::bidirectional_iterator_tag, IteratorCategoryT>::value,
47  };
48 
49 public:
50  DerivedT operator+(DifferenceTypeT n) const {
51  static_assert(
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(
61  "The '+' operator is only defined for random access iterators.");
62  return i + n;
63  }
64  DerivedT operator-(DifferenceTypeT n) const {
65  static_assert(
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  }
72 
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(
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(
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  }
95 
96  bool operator!=(const DerivedT &RHS) const {
97  return !static_cast<const DerivedT *>(this)->operator==(RHS);
98  }
99 
100  bool operator>(const DerivedT &RHS) const {
101  static_assert(
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(
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(
116  "Relational operators are only defined for random access iterators.");
117  return !static_cast<const DerivedT *>(this)->operator<(RHS);
118  }
119 
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 };
129 
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>>
146  : public iterator_facade_base<DerivedT, IteratorCategoryT, T,
147  DifferenceTypeT, PointerT, ReferenceT> {
148  typedef typename iterator_adaptor_base::iterator_facade_base BaseT;
149 
150 protected:
151  WrappedIteratorT I;
152 
153  iterator_adaptor_base() = default;
154 
155  template <typename U>
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)) {}
164 
165  const WrappedIteratorT &wrapped() const { return I; }
166 
167 public:
168  typedef DifferenceTypeT difference_type;
169 
171  static_assert(
172  BaseT::IsRandomAccess,
173  "The '+=' operator is only defined for random access iterators.");
174  I += n;
175  return *static_cast<DerivedT *>(this);
176  }
178  static_assert(
179  BaseT::IsRandomAccess,
180  "The '-=' operator is only defined for random access iterators.");
181  I -= n;
182  return *static_cast<DerivedT *>(this);
183  }
184  using BaseT::operator-;
185  difference_type operator-(const DerivedT &RHS) const {
186  static_assert(
187  BaseT::IsRandomAccess,
188  "The '-' operator is only defined for random access iterators.");
189  return I - RHS.I;
190  }
191 
192  // We have to explicitly provide ++ and -- rather than letting the facade
193  // forward to += because WrappedIteratorT might not support +=.
194  using BaseT::operator++;
195  DerivedT &operator++() {
196  ++I;
197  return *static_cast<DerivedT *>(this);
198  }
199  using BaseT::operator--;
200  DerivedT &operator--() {
201  static_assert(
202  BaseT::IsBidirectional,
203  "The decrement operator is only defined for bidirectional iterators.");
204  --I;
205  return *static_cast<DerivedT *>(this);
206  }
207 
208  bool operator==(const DerivedT &RHS) const { return I == RHS.I; }
209  bool operator<(const DerivedT &RHS) const {
210  static_assert(
211  BaseT::IsRandomAccess,
212  "Relational operators are only defined for random access iterators.");
213  return I < RHS.I;
214  }
215 
216  ReferenceT operator*() const { return *I; }
217 };
218 
219 /// \brief An iterator type that allows iterating over the pointees via some
220 /// other iterator.
221 ///
222 /// The typical usage of this is to expose a type that iterates over Ts, but
223 /// which is implemented with some iterator over T*s:
224 ///
225 /// \code
226 /// typedef pointee_iterator<SmallVectorImpl<T *>::iterator> iterator;
227 /// \endcode
228 template <typename WrappedIteratorT,
229  typename T = typename std::remove_reference<
230  decltype(**std::declval<WrappedIteratorT>())>::type>
233  pointee_iterator<WrappedIteratorT>, WrappedIteratorT,
234  typename std::iterator_traits<WrappedIteratorT>::iterator_category,
235  T> {
236  pointee_iterator() = default;
237  template <typename U>
239  : pointee_iterator::iterator_adaptor_base(std::forward<U &&>(u)) {}
240 
241  T &operator*() const { return **this->I; }
242 };
243 
244 }
245 
246 #endif
WrappedIteratorT I
Definition: iterator.h:151
DifferenceTypeT difference_type
Definition: iterator.h:168
difference_type operator-(const DerivedT &RHS) const
Definition: iterator.h:185
bool operator>(const DerivedT &RHS) const
Definition: iterator.h:100
bool operator>=(const DerivedT &RHS) const
Definition: iterator.h:113
DerivedT operator-(DifferenceTypeT n) const
Definition: iterator.h:64
DerivedT operator+(DifferenceTypeT n) const
Definition: iterator.h:50
DerivedT & operator--()
Definition: iterator.h:81
bool operator==(const DerivedT &RHS) const
Definition: iterator.h:208
bool operator<=(const DerivedT &RHS) const
Definition: iterator.h:107
DerivedT & operator+=(difference_type n)
Definition: iterator.h:170
#define T
CRTP base class which implements the entire standard iterator facade in terms of a minimal subset of ...
Definition: iterator.h:38
bool operator!=(const DerivedT &RHS) const
Definition: iterator.h:96
ReferenceT operator*() const
Definition: iterator.h:216
T & operator*() const
Definition: iterator.h:241
CRTP base class for adapting an iterator to a different type.
Definition: iterator.h:145
iterator_adaptor_base(U &&u, typename std::enable_if< !std::is_base_of< typename std::remove_cv< typename std::remove_reference< U >::type >::type, DerivedT >::value, int >::type=0)
Definition: iterator.h:156
friend DerivedT operator+(DifferenceTypeT n, const DerivedT &i)
Definition: iterator.h:58
ReferenceT operator[](DifferenceTypeT n) const
Definition: iterator.h:123
DerivedT & operator++()
Definition: iterator.h:73
An iterator type that allows iterating over the pointees via some other iterator. ...
Definition: iterator.h:231
const WrappedIteratorT & wrapped() const
Definition: iterator.h:165
DerivedT operator--(int)
Definition: iterator.h:87
DerivedT operator++(int)
Definition: iterator.h:76
DerivedT & operator-=(difference_type n)
Definition: iterator.h:177
PointerT operator->() const
Definition: iterator.h:120
bool operator<(const DerivedT &RHS) const
Definition: iterator.h:209