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 &> 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 }; 48 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 } 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( 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 } 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( 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 } 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>> 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; 149 150 protected: 151 WrappedIteratorT I; 152 153 iterator_adaptor_base() = default; 154 155 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) I(std::forward<U &&> (u))163 : I(std::forward<U &&>(u)) {} 164 wrapped()165 const WrappedIteratorT &wrapped() const { return I; } 166 167 public: 168 typedef DifferenceTypeT difference_type; 169 170 DerivedT &operator+=(difference_type n) { 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 } 177 DerivedT &operator-=(difference_type n) { 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> 231 struct pointee_iterator 232 : iterator_adaptor_base< 233 pointee_iterator<WrappedIteratorT>, WrappedIteratorT, 234 typename std::iterator_traits<WrappedIteratorT>::iterator_category, 235 T> { 236 pointee_iterator() = default; 237 template <typename U> pointee_iteratorpointee_iterator238 pointee_iterator(U &&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 247