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1 // Copyright (c) 2013 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 // | |
5 // This is a simplistic insertion-ordered map. It behaves similarly to an STL | |
6 // map, but only implements a small subset of the map's methods. Internally, we | |
7 // just keep a map and a list going in parallel. | |
8 // | |
9 // This class provides no thread safety guarantees, beyond what you would | |
10 // normally see with std::list. | |
11 // | |
12 // Iterators should be stable in the face of mutations, except for an | |
13 // iterator pointing to an element that was just deleted. | |
14 | |
15 #ifndef UTIL_GTL_LINKED_HASH_MAP_H_ | |
16 #define UTIL_GTL_LINKED_HASH_MAP_H_ | |
17 | |
18 #include <list> | |
19 #include <utility> | |
20 | |
21 #include "base/containers/hash_tables.h" | |
22 #include "base/logging.h" | |
23 | |
24 // This holds a list of pair<Key, Value> items. This list is what gets | |
25 // traversed, and it's iterators from this list that we return from | |
26 // begin/end/find. | |
27 // | |
28 // We also keep a map<Key, list::iterator> for find. Since std::list is a | |
29 // doubly-linked list, the iterators should remain stable. | |
30 template<class Key, class Value> | |
31 class linked_hash_map { | |
32 private: | |
33 typedef std::list<std::pair<Key, Value> > ListType; | |
34 typedef base::hash_map<Key, typename ListType::iterator> MapType; | |
35 | |
36 public: | |
37 typedef typename ListType::iterator iterator; | |
38 typedef typename ListType::reverse_iterator reverse_iterator; | |
39 typedef typename ListType::const_iterator const_iterator; | |
40 typedef typename ListType::const_reverse_iterator const_reverse_iterator; | |
41 typedef typename MapType::key_type key_type; | |
42 typedef typename ListType::value_type value_type; | |
43 typedef typename ListType::size_type size_type; | |
44 | |
45 linked_hash_map() : map_(), list_() { | |
46 } | |
47 | |
48 // Returns an iterator to the first (insertion-ordered) element. Like a map, | |
49 // this can be dereferenced to a pair<Key, Value>. | |
50 iterator begin() { | |
51 return list_.begin(); | |
52 } | |
53 const_iterator begin() const { | |
54 return list_.begin(); | |
55 } | |
56 | |
57 // Returns an iterator beyond the last element. | |
58 iterator end() { | |
59 return list_.end(); | |
60 } | |
61 const_iterator end() const { | |
62 return list_.end(); | |
63 } | |
64 | |
65 // Returns an iterator to the last (insertion-ordered) element. Like a map, | |
66 // this can be dereferenced to a pair<Key, Value>. | |
67 reverse_iterator rbegin() { | |
68 return list_.rbegin(); | |
69 } | |
70 const_reverse_iterator rbegin() const { | |
71 return list_.rbegin(); | |
72 } | |
73 | |
74 // Returns an iterator beyond the first element. | |
75 reverse_iterator rend() { | |
76 return list_.rend(); | |
77 } | |
78 const_reverse_iterator rend() const { | |
79 return list_.rend(); | |
80 } | |
81 | |
82 // Front and back accessors common to many stl containers. | |
83 | |
84 // Returns the earliest-inserted element | |
85 const value_type& front() const { | |
86 return list_.front(); | |
87 } | |
88 | |
89 // Returns the earliest-inserted element. | |
90 value_type& front() { | |
91 return list_.front(); | |
92 } | |
93 | |
94 // Returns the most-recently-inserted element. | |
95 const value_type& back() const { | |
96 return list_.back(); | |
97 } | |
98 | |
99 // Returns the most-recently-inserted element. | |
100 value_type& back() { | |
101 return list_.back(); | |
102 } | |
103 | |
104 // Clears the map of all values. | |
105 void clear() { | |
106 map_.clear(); | |
107 list_.clear(); | |
108 } | |
109 | |
110 // Returns true iff the map is empty. | |
111 bool empty() const { | |
112 return list_.empty(); | |
113 } | |
114 | |
115 // Erases values with the provided key. Returns the number of elements | |
116 // erased. In this implementation, this will be 0 or 1. | |
117 size_type erase(const Key& key) { | |
118 typename MapType::iterator found = map_.find(key); | |
119 if (found == map_.end()) return 0; | |
120 | |
121 list_.erase(found->second); | |
122 map_.erase(found); | |
123 | |
124 return 1; | |
125 } | |
126 | |
127 // Erases values with the provided iterator. If the provided iterator is | |
128 // invalid or there is inconsistency between the map and list, a CHECK() error | |
129 // will occur. | |
130 void erase(iterator position) { | |
131 typename MapType::iterator found = map_.find(position->first); | |
132 CHECK(found->second == position) | |
133 << "Inconsisent iterator for map and list, or the iterator is invalid."; | |
134 | |
135 list_.erase(position); | |
136 map_.erase(found); | |
137 } | |
138 | |
139 // Erases values between first and last, not including last. | |
140 void erase(iterator first, iterator last) { | |
141 while (first != last && first != end()) { | |
142 erase(first++); | |
143 } | |
144 } | |
145 | |
146 // Finds the element with the given key. Returns an iterator to the | |
147 // value found, or to end() if the value was not found. Like a map, this | |
148 // iterator points to a pair<Key, Value>. | |
149 iterator find(const Key& key) { | |
150 typename MapType::iterator found = map_.find(key); | |
151 if (found == map_.end()) { | |
152 return end(); | |
153 } | |
154 return found->second; | |
155 } | |
156 | |
157 const_iterator find(const Key& key) const { | |
158 typename MapType::const_iterator found = map_.find(key); | |
159 if (found == map_.end()) { | |
160 return end(); | |
161 } | |
162 return found->second; | |
163 } | |
164 | |
165 // Returns the bounds of a range that includes all the elements in the | |
166 // container with a key that compares equal to x. | |
167 std::pair<iterator, iterator> equal_range(const key_type& key) { | |
168 std::pair<typename MapType::iterator, typename MapType::iterator> eq_range = | |
169 map_.equal_range(key); | |
170 | |
171 return std::make_pair(eq_range.first->second, eq_range.second->second); | |
172 } | |
173 | |
174 std::pair<const_iterator, const_iterator> equal_range( | |
175 const key_type& key) const { | |
176 std::pair<typename MapType::const_iterator, | |
177 typename MapType::const_iterator> eq_range = | |
178 map_.equal_range(key); | |
179 const const_iterator& start_iter = eq_range.first != map_.end() ? | |
180 eq_range.first->second : end(); | |
181 const const_iterator& end_iter = eq_range.second != map_.end() ? | |
182 eq_range.second->second : end(); | |
183 | |
184 return std::make_pair(start_iter, end_iter); | |
185 } | |
186 | |
187 // Returns the value mapped to key, or an inserted iterator to that position | |
188 // in the map. | |
189 Value& operator[](const key_type& key) { | |
190 return (*((this->insert(std::make_pair(key, Value()))).first)).second; | |
191 } | |
192 | |
193 // Inserts an element into the map | |
194 std::pair<iterator, bool> insert(const std::pair<Key, Value>& pair) { | |
195 // First make sure the map doesn't have a key with this value. If it does, | |
196 // return a pair with an iterator to it, and false indicating that we | |
197 // didn't insert anything. | |
198 typename MapType::iterator found = map_.find(pair.first); | |
199 if (found != map_.end()) return std::make_pair(found->second, false); | |
200 | |
201 // Otherwise, insert into the list first. | |
202 list_.push_back(pair); | |
203 | |
204 // Obtain an iterator to the newly added element. We do -- instead of - | |
205 // since list::iterator doesn't implement operator-(). | |
206 typename ListType::iterator last = list_.end(); | |
207 --last; | |
208 | |
209 CHECK(map_.insert(std::make_pair(pair.first, last)).second) | |
210 << "Map and list are inconsistent"; | |
211 | |
212 return std::make_pair(last, true); | |
213 } | |
214 | |
215 size_type size() const { | |
216 return list_.size(); | |
217 } | |
218 | |
219 void swap(linked_hash_map& other) { | |
220 map_.swap(other.map_); | |
221 list_.swap(other.list_); | |
222 } | |
223 | |
224 private: | |
225 // The map component, used for speedy lookups | |
226 MapType map_; | |
227 | |
228 // The list component, used for maintaining insertion order | |
229 ListType list_; | |
230 }; | |
231 | |
232 #endif // UTIL_GTL_LINKED_HASH_MAP_H_ | |
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