Move DoubleLinkedQueue from coreimpl to core.

lib/core/queue.dart

Index: lib/core/queue.dart
diff --git a/lib/core/queue.dart b/lib/core/queue.dart
index ecdfe3641d6057297258c8e91abbdbdd40b7c3c3..bf1e49c2113bbc97e3066b5a9e98891c697aee05 100644
--- a/lib/core/queue.dart
+++ b/lib/core/queue.dart
@@ -70,3 +70,269 @@ abstract class Queue<E> extends Collection<E> {
    */
   void clear();
 }
+
+
+/**
+ * An entry in a doubly linked list. It contains a pointer to the next
+ * entry, the previous entry, and the boxed element.
+ *
+ * WARNING: This class is temporary located in dart:core. It'll be removed
+ * at some point in the near future.
+ */
+class DoubleLinkedQueueEntry<E> {
+  DoubleLinkedQueueEntry<E> _previous;
+  DoubleLinkedQueueEntry<E> _next;
+  E _element;
+
+  DoubleLinkedQueueEntry(E e) {
+    _element = e;
+  }
+
+  void _link(DoubleLinkedQueueEntry<E> p,
+             DoubleLinkedQueueEntry<E> n) {
+    _next = n;
+    _previous = p;
+    p._next = this;
+    n._previous = this;
+  }
+
+  void append(E e) {
+    new DoubleLinkedQueueEntry<E>(e)._link(this, _next);
+  }
+
+  void prepend(E e) {
+    new DoubleLinkedQueueEntry<E>(e)._link(_previous, this);
+  }
+
+  E remove() {
+    _previous._next = _next;
+    _next._previous = _previous;
+    _next = null;
+    _previous = null;
+    return _element;
+  }
+
+  DoubleLinkedQueueEntry<E> _asNonSentinelEntry() {
+    return this;
+  }
+
+  DoubleLinkedQueueEntry<E> previousEntry() {
+    return _previous._asNonSentinelEntry();
+  }
+
+  DoubleLinkedQueueEntry<E> nextEntry() {
+    return _next._asNonSentinelEntry();
+  }
+
+  E get element {
+    return _element;
+  }
+
+  void set element(E e) {
+    _element = e;
+  }
+}
+
+/**
+ * A sentinel in a double linked list is used to manipulate the list
+ * at both ends. A double linked list has exactly one sentinel, which
+ * is the only entry when the list is constructed. Initially, a
+ * sentinel has its next and previous entry point to itself. A
+ * sentinel does not box any user element.
+ */
+class _DoubleLinkedQueueEntrySentinel<E> extends DoubleLinkedQueueEntry<E> {
+  _DoubleLinkedQueueEntrySentinel() : super(null) {
+    _link(this, this);
+  }
+
+  E remove() {
+    throw new StateError("Empty queue");
+  }
+
+  DoubleLinkedQueueEntry<E> _asNonSentinelEntry() {
+    return null;
+  }
+
+  void set element(E e) {
+    // This setter is unreachable.
+    assert(false);
+  }
+
+  E get element {
+    throw new StateError("Empty queue");
+  }
+}
+
+/**
+ * Implementation of a double linked list that box list elements into
+ * DoubleLinkedQueueEntry objects.
+ *
+ * WARNING: This class is temporary located in dart:core. It'll be removed
+ * at some point in the near future.
+ */
+class DoubleLinkedQueue<E> implements Queue<E> {
+  _DoubleLinkedQueueEntrySentinel<E> _sentinel;
+
+  DoubleLinkedQueue() {
+    _sentinel = new _DoubleLinkedQueueEntrySentinel<E>();
+  }
+
+  factory DoubleLinkedQueue.from(Iterable<E> other) {
+    Queue<E> list = new DoubleLinkedQueue();
+    for (final e in other) {
+      list.addLast(e);
+    }
+    return list;
+  }
+
+  void addLast(E value) {
+    _sentinel.prepend(value);
+  }
+
+  void addFirst(E value) {
+    _sentinel.append(value);
+  }
+
+  void add(E value) {
+    addLast(value);
+  }
+
+  void addAll(Collection<E> collection) {
+    for (final e in collection) {
+      add(e);
+    }
+  }
+
+  E removeLast() {
+    return _sentinel._previous.remove();
+  }
+
+  E removeFirst() {
+    return _sentinel._next.remove();
+  }
+
+  E get first {
+    return _sentinel._next.element;
+  }
+
+  E get last {
+    return _sentinel._previous.element;
+  }
+
+  DoubleLinkedQueueEntry<E> lastEntry() {
+    return _sentinel.previousEntry();
+  }
+
+  DoubleLinkedQueueEntry<E> firstEntry() {
+    return _sentinel.nextEntry();
+  }
+
+  int get length {
+    int counter = 0;
+    forEach(void _(E element) { counter++; });
+    return counter;
+  }
+
+  bool get isEmpty {
+    return (_sentinel._next === _sentinel);
+  }
+
+  void clear() {
+    _sentinel._next = _sentinel;
+    _sentinel._previous = _sentinel;
+  }
+
+  void forEach(void f(E element)) {
+    DoubleLinkedQueueEntry<E> entry = _sentinel._next;
+    while (entry !== _sentinel) {
+      DoubleLinkedQueueEntry<E> nextEntry = entry._next;
+      f(entry._element);
+      entry = nextEntry;
+    }
+  }
+
+  void forEachEntry(void f(DoubleLinkedQueueEntry<E> element)) {
+    DoubleLinkedQueueEntry<E> entry = _sentinel._next;
+    while (entry !== _sentinel) {
+      DoubleLinkedQueueEntry<E> nextEntry = entry._next;
+      f(entry);
+      entry = nextEntry;
+    }
+  }
+
+  bool every(bool f(E element)) {
+    DoubleLinkedQueueEntry<E> entry = _sentinel._next;
+    while (entry !== _sentinel) {
+      DoubleLinkedQueueEntry<E> nextEntry = entry._next;
+      if (!f(entry._element)) return false;
+      entry = nextEntry;
+    }
+    return true;
+  }
+
+  bool some(bool f(E element)) {
+    DoubleLinkedQueueEntry<E> entry = _sentinel._next;
+    while (entry !== _sentinel) {
+      DoubleLinkedQueueEntry<E> nextEntry = entry._next;
+      if (f(entry._element)) return true;
+      entry = nextEntry;
+    }
+    return false;
+  }
+
+  Queue map(f(E element)) {
+    Queue other = new Queue();
+    DoubleLinkedQueueEntry<E> entry = _sentinel._next;
+    while (entry !== _sentinel) {
+      DoubleLinkedQueueEntry<E> nextEntry = entry._next;
+      other.addLast(f(entry._element));
+      entry = nextEntry;
+    }
+    return other;
+  }
+
+  Dynamic reduce(Dynamic initialValue,
+                 Dynamic combine(Dynamic previousValue, E element)) {
+    return Collections.reduce(this, initialValue, combine);
+  }
+
+  Queue<E> filter(bool f(E element)) {
+    Queue<E> other = new Queue<E>();
+    DoubleLinkedQueueEntry<E> entry = _sentinel._next;
+    while (entry !== _sentinel) {
+      DoubleLinkedQueueEntry<E> nextEntry = entry._next;
+      if (f(entry._element)) other.addLast(entry._element);
+      entry = nextEntry;
+    }
+    return other;
+  }
+
+  _DoubleLinkedQueueIterator<E> iterator() {
+    return new _DoubleLinkedQueueIterator<E>(_sentinel);
+  }
+
+  String toString() {
+    return Collections.collectionToString(this);
+  }
+}
+
+class _DoubleLinkedQueueIterator<E> implements Iterator<E> {
+  final _DoubleLinkedQueueEntrySentinel<E> _sentinel;
+  DoubleLinkedQueueEntry<E> _currentEntry;
+
+  _DoubleLinkedQueueIterator(_DoubleLinkedQueueEntrySentinel this._sentinel) {
+    _currentEntry = _sentinel;
+  }
+
+  bool get hasNext {
+    return _currentEntry._next !== _sentinel;
+  }
+
+  E next() {
+    if (!hasNext) {
+      throw new StateError("No more elements");
+    }
+    _currentEntry = _currentEntry._next;
+    return _currentEntry.element;
+  }
+}