linked_list.h | Explore in Territory

// Copyright 2009 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_CONTAINERS_LINKED_LIST_H_
#define BASE_CONTAINERS_LINKED_LIST_H_

#include "base/base_export.h"
#include "base/memory/raw_ptr_exclusion.h"

// Simple LinkedList type. (See the Q&A section to understand how this
// differs from std::list).
//
// To use, start by declaring the class which will be contained in the linked
// list, as extending LinkNode (this gives it next/previous pointers).
//
//   class MyNodeType : public LinkNode<MyNodeType> {
//     ...
//   };
//
// Next, to keep track of the list's head/tail, use a LinkedList instance:
//
//   LinkedList<MyNodeType> list;
//
// To add elements to the list, use any of LinkedList::Append,
// LinkNode::InsertBefore, or LinkNode::InsertAfter:
//
//   LinkNode<MyNodeType>* n1 = ...;
//   LinkNode<MyNodeType>* n2 = ...;
//   LinkNode<MyNodeType>* n3 = ...;
//
//   list.Append(n1);
//   list.Append(n3);
//   n2->InsertBefore(n3);
//
// Lastly, to iterate through the linked list forwards:
//
//   for (LinkNode<MyNodeType>* node = list.head();
//        node != list.end();
//        node = node->next()) {
//     MyNodeType* value = node->value();
//     ...
//   }
//
// Or to iterate the linked list backwards:
//
//   for (LinkNode<MyNodeType>* node = list.tail();
//        node != list.end();
//        node = node->previous()) {
//     MyNodeType* value = node->value();
//     ...
//   }
//
// Questions and Answers:
//
// Q. Should I use std::list or base::LinkedList?
//
// A. The main reason to use base::LinkedList over std::list is
//    performance. If you don't care about the performance differences
//    then use an STL container, as it makes for better code readability.
//
//    Comparing the performance of base::LinkedList<T> to std::list<T*>:
//
//    * Erasing an element of type T* from base::LinkedList<T> is
//      an O(1) operation. Whereas for std::list<T*> it is O(n).
//      That is because with std::list<T*> you must obtain an
//      iterator to the T* element before you can call erase(iterator).
//
//    * Insertion operations with base::LinkedList<T> never require
//      heap allocations.
//
// Q. How does base::LinkedList implementation differ from std::list?
//
// A. Doubly-linked lists are made up of nodes that contain "next" and
//    "previous" pointers that reference other nodes in the list.
//
//    With base::LinkedList<T>, the type being inserted already reserves
//    space for the "next" and "previous" pointers (base::LinkNode<T>*).
//    Whereas with std::list<T> the type can be anything, so the implementation
//    needs to glue on the "next" and "previous" pointers using
//    some internal node type.

namespace base {

namespace internal {

// Base class for LinkNode<T> type
class BASE_EXPORT LinkNodeBase { … };

}  // namespace internal

template <typename T>
class LinkNode : public internal::LinkNodeBase { … };

template <typename T>
class LinkedList { … };

}  // namespace base

#endif  // BASE_CONTAINERS_LINKED_LIST_H_
chromium/base/containers/linked_list.h
