Use iterator, moveNext(), current.

sdk/lib/core/queue.dart

Index: sdk/lib/core/queue.dart
diff --git a/sdk/lib/core/queue.dart b/sdk/lib/core/queue.dart
index 91fcfce6e4d34100b795d2ffbae76773e0dbdb6c..8b2c9673a0c586855ed7894ec5d5d0bd02919fc0 100644
--- a/sdk/lib/core/queue.dart
+++ b/sdk/lib/core/queue.dart
@@ -307,7 +307,7 @@ class DoubleLinkedQueue<E> implements Queue<E> {
     return other;
   }
 
-  _DoubleLinkedQueueIterator<E> iterator() {
+  _DoubleLinkedQueueIterator<E> get iterator {
     return new _DoubleLinkedQueueIterator<E>(_sentinel);
   }
 
@@ -318,21 +318,22 @@ class DoubleLinkedQueue<E> implements Queue<E> {
 
 class _DoubleLinkedQueueIterator<E> implements Iterator<E> {
   final _DoubleLinkedQueueEntrySentinel<E> _sentinel;
-  DoubleLinkedQueueEntry<E> _currentEntry;
+  DoubleLinkedQueueEntry<E> _currentEntry = null;
 
-  _DoubleLinkedQueueIterator(_DoubleLinkedQueueEntrySentinel this._sentinel) {
-    _currentEntry = _sentinel;
-  }
+  _DoubleLinkedQueueIterator(this._sentinel);
 
-  bool get hasNext {
-    return !identical(_currentEntry._next, _sentinel);
+  bool moveNext() {
+    if (identical(_currentEntry, _sentinel)) return false;

[Lasse Reichstein Nielsen, 2012/11/15 10:24:37]

The 'null' represents the initial state, right?
Documentation, please!

How about a boolean named '_done' that gets set when you move to the sentinel:
bool moveNext() {
  if (_done) return false;
  _currentEntry = _currentEntry._next;
  _done = identical(_currentEntry, _sentinel);
  return !_done;
}

Do use identical when it's what we really mean (and it is for linked lists and
sentinels in general), so I don't have to wonder what happens if the Entry class
implements operator==.
  

[floitsch, 2012/11/16 17:51:58]

in theory there is no need to use identical since the elements are
DoubleLinkedQueueEntrys.
added comment, and used identical below.
this will become different with the new approach.

+    if (_currentEntry == null) _currentEntry = _sentinel;
+    _currentEntry = _currentEntry._next;
+    return _currentEntry != _sentinel;
   }
 
-  E next() {
-    if (!hasNext) {
-      throw new StateError("No more elements");
+  E get current {
+    if (_currentEntry != null && _currentEntry != _sentinel) {
+      return _currentEntry.element;
     }
-    _currentEntry = _currentEntry._next;
-    return _currentEntry.element;
+    // TODO(floitsch): adapt error message.
+    throw new StateError("No more elements");
   }
 }