Don't use `LinkedList` in the core libraries anymore.

sdk/lib/internal/linked_list.dart

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of dart._internal;
+
+/// A rudimentary linked list.
+class LinkedList<T extends LinkedListEntry<T>> extends IterableBase<T> {
+  T first;
+  T last;
+  int length = 0;
+
+  bool get isEmpty => length == 0;
+
+  /**
+   * Adds [newLast] to the end of this linked list.
+   */
+  void add(T newLast) {
+    assert(newLast._next == null && newLast._previous == null);
+    if (last != null) {
+      assert(last._next == null);
+      last._next = newLast;
+    } else {
+      first = newLast;
+    }
+    newLast._previous = last;
+    last = newLast;
+    last._list = this;
+    length++;
+  }
+
+  /**
+   * Adds [newFirst] to the beginning of this linked list.
+   */
+  void addFirst(T newFirst) {
+    if (first != null) {
+      assert(first._previous == null);
+      first._previous = newFirst;
+    } else {
+      last = newFirst;
+    }
+    newFirst._next = first;
+    first = newFirst;
+    first._list = this;
+    length++;
+  }
+
+  /**
+   * Removes the given [node] from this list.
+   *
+   * If the entry is not in this linked list nothing happens.
+   *
+   * Also see [LinkedListEntry.unlink].
+   */
+  void remove(T node) {
+    if (node._list != this) return;
+    length--;
+    if (node._previous == null) {
+      assert(identical(node, first));
+      first = node._next;
+    } else {
+      node._previous._next = node._next;
+    }
+    if (node._next == null) {
+      assert(identical(node, last));
+      last = node._previous;
+    } else {
+      node._next._previous = node._previous;
+    }
+    node._next = node._previous = null;
+    node._list = null;
+  }
+
+  Iterator<T> get iterator => new _LinkedListIterator<T>(this);
+}
+
+class LinkedListEntry<T extends LinkedListEntry<T>> {
+  T _next;
+  T _previous;
+  LinkedList<T> _list;
+
+  /**
+   * Unlinks the element from its linked list.
+   *
+   * If the entry is not in a linked list, does nothing. Otherwise, this
+   * is equivalent to calling [LinkedList.remove] on the list this entry
+   * is currently in.
+   */
+  void unlink() {
+    if (_list == null) return;
+    _list.remove(this);
+  }
+}
+
+class _LinkedListIterator<T extends LinkedListEntry<T>> implements Iterator<T> {
+  /// The current element of the iterator.
+  // This field is writeable, but should only read by users of this class.
+  T current;
+
+  /// The list the iterator iterates over.
+  ///
+  /// Set to [null] if the provided list was empty (indicating that there were
+  /// no entries to iterate over).
+  ///
+  /// Set to [null] as soon as [moveNext] was invoked (indicating that the
+  /// iterator has to work with [current] from now on.
+  LinkedList<T> _list;
+
+  _LinkedListIterator(this._list) {
+    if (_list.length == 0) _list = null;
+  }
+
+  bool moveNext() {
+    // current is null if the iterator hasn't started iterating, or if the
+    // iteration is finished. In the first case, the [_list] field is not null.
+    if (current == null) {
+      if (_list == null) return false;
+      assert(_list.length > 0);
+      current = _list.first;
+      _list = null;
+      return true;
+    }
+    current = current._next;
+    return current != null;
+  }
+}