James Robinson | 646469d | 2014-10-03 15:33:28 -0700 | [diff] [blame] | 1 | // Copyright (c) 2009 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 | #ifndef BASE_CONTAINERS_LINKED_LIST_H_ |
| 6 | #define BASE_CONTAINERS_LINKED_LIST_H_ |
| 7 | |
| 8 | #include "base/macros.h" |
| 9 | |
| 10 | // Simple LinkedList type. (See the Q&A section to understand how this |
| 11 | // differs from std::list). |
| 12 | // |
| 13 | // To use, start by declaring the class which will be contained in the linked |
| 14 | // list, as extending LinkNode (this gives it next/previous pointers). |
| 15 | // |
| 16 | // class MyNodeType : public LinkNode<MyNodeType> { |
| 17 | // ... |
| 18 | // }; |
| 19 | // |
| 20 | // Next, to keep track of the list's head/tail, use a LinkedList instance: |
| 21 | // |
| 22 | // LinkedList<MyNodeType> list; |
| 23 | // |
| 24 | // To add elements to the list, use any of LinkedList::Append, |
| 25 | // LinkNode::InsertBefore, or LinkNode::InsertAfter: |
| 26 | // |
| 27 | // LinkNode<MyNodeType>* n1 = ...; |
| 28 | // LinkNode<MyNodeType>* n2 = ...; |
| 29 | // LinkNode<MyNodeType>* n3 = ...; |
| 30 | // |
| 31 | // list.Append(n1); |
| 32 | // list.Append(n3); |
| 33 | // n3->InsertBefore(n3); |
| 34 | // |
| 35 | // Lastly, to iterate through the linked list forwards: |
| 36 | // |
| 37 | // for (LinkNode<MyNodeType>* node = list.head(); |
| 38 | // node != list.end(); |
| 39 | // node = node->next()) { |
| 40 | // MyNodeType* value = node->value(); |
| 41 | // ... |
| 42 | // } |
| 43 | // |
| 44 | // Or to iterate the linked list backwards: |
| 45 | // |
| 46 | // for (LinkNode<MyNodeType>* node = list.tail(); |
| 47 | // node != list.end(); |
| 48 | // node = node->previous()) { |
| 49 | // MyNodeType* value = node->value(); |
| 50 | // ... |
| 51 | // } |
| 52 | // |
| 53 | // Questions and Answers: |
| 54 | // |
| 55 | // Q. Should I use std::list or base::LinkedList? |
| 56 | // |
| 57 | // A. The main reason to use base::LinkedList over std::list is |
| 58 | // performance. If you don't care about the performance differences |
| 59 | // then use an STL container, as it makes for better code readability. |
| 60 | // |
| 61 | // Comparing the performance of base::LinkedList<T> to std::list<T*>: |
| 62 | // |
| 63 | // * Erasing an element of type T* from base::LinkedList<T> is |
| 64 | // an O(1) operation. Whereas for std::list<T*> it is O(n). |
| 65 | // That is because with std::list<T*> you must obtain an |
| 66 | // iterator to the T* element before you can call erase(iterator). |
| 67 | // |
| 68 | // * Insertion operations with base::LinkedList<T> never require |
| 69 | // heap allocations. |
| 70 | // |
| 71 | // Q. How does base::LinkedList implementation differ from std::list? |
| 72 | // |
| 73 | // A. Doubly-linked lists are made up of nodes that contain "next" and |
| 74 | // "previous" pointers that reference other nodes in the list. |
| 75 | // |
| 76 | // With base::LinkedList<T>, the type being inserted already reserves |
| 77 | // space for the "next" and "previous" pointers (base::LinkNode<T>*). |
| 78 | // Whereas with std::list<T> the type can be anything, so the implementation |
| 79 | // needs to glue on the "next" and "previous" pointers using |
| 80 | // some internal node type. |
| 81 | |
| 82 | namespace base { |
| 83 | |
| 84 | template <typename T> |
| 85 | class LinkNode { |
| 86 | public: |
| 87 | LinkNode() : previous_(NULL), next_(NULL) {} |
| 88 | LinkNode(LinkNode<T>* previous, LinkNode<T>* next) |
| 89 | : previous_(previous), next_(next) {} |
| 90 | |
| 91 | // Insert |this| into the linked list, before |e|. |
| 92 | void InsertBefore(LinkNode<T>* e) { |
| 93 | this->next_ = e; |
| 94 | this->previous_ = e->previous_; |
| 95 | e->previous_->next_ = this; |
| 96 | e->previous_ = this; |
| 97 | } |
| 98 | |
| 99 | // Insert |this| into the linked list, after |e|. |
| 100 | void InsertAfter(LinkNode<T>* e) { |
| 101 | this->next_ = e->next_; |
| 102 | this->previous_ = e; |
| 103 | e->next_->previous_ = this; |
| 104 | e->next_ = this; |
| 105 | } |
| 106 | |
| 107 | // Remove |this| from the linked list. |
| 108 | void RemoveFromList() { |
| 109 | this->previous_->next_ = this->next_; |
| 110 | this->next_->previous_ = this->previous_; |
| 111 | // next() and previous() return non-NULL if and only this node is not in any |
| 112 | // list. |
| 113 | this->next_ = NULL; |
| 114 | this->previous_ = NULL; |
| 115 | } |
| 116 | |
| 117 | LinkNode<T>* previous() const { |
| 118 | return previous_; |
| 119 | } |
| 120 | |
| 121 | LinkNode<T>* next() const { |
| 122 | return next_; |
| 123 | } |
| 124 | |
| 125 | // Cast from the node-type to the value type. |
| 126 | const T* value() const { |
| 127 | return static_cast<const T*>(this); |
| 128 | } |
| 129 | |
| 130 | T* value() { |
| 131 | return static_cast<T*>(this); |
| 132 | } |
| 133 | |
| 134 | private: |
| 135 | LinkNode<T>* previous_; |
| 136 | LinkNode<T>* next_; |
| 137 | |
| 138 | DISALLOW_COPY_AND_ASSIGN(LinkNode); |
| 139 | }; |
| 140 | |
| 141 | template <typename T> |
| 142 | class LinkedList { |
| 143 | public: |
| 144 | // The "root" node is self-referential, and forms the basis of a circular |
| 145 | // list (root_.next() will point back to the start of the list, |
| 146 | // and root_->previous() wraps around to the end of the list). |
| 147 | LinkedList() : root_(&root_, &root_) {} |
| 148 | |
| 149 | // Appends |e| to the end of the linked list. |
| 150 | void Append(LinkNode<T>* e) { |
| 151 | e->InsertBefore(&root_); |
| 152 | } |
| 153 | |
| 154 | LinkNode<T>* head() const { |
| 155 | return root_.next(); |
| 156 | } |
| 157 | |
| 158 | LinkNode<T>* tail() const { |
| 159 | return root_.previous(); |
| 160 | } |
| 161 | |
| 162 | const LinkNode<T>* end() const { |
| 163 | return &root_; |
| 164 | } |
| 165 | |
| 166 | bool empty() const { return head() == end(); } |
| 167 | |
| 168 | private: |
| 169 | LinkNode<T> root_; |
| 170 | |
| 171 | DISALLOW_COPY_AND_ASSIGN(LinkedList); |
| 172 | }; |
| 173 | |
| 174 | } // namespace base |
| 175 | |
| 176 | #endif // BASE_CONTAINERS_LINKED_LIST_H_ |