Move some core classes to collection library.

sdk/lib/collection/iterator.dart

+// Copyright (c) 2012, 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.collection;
+
+/**
+ * The [HasNextIterator] class wraps an [Iterator] and provides methods to
+ * iterate over an object using `hasNext` and `next`.
+ *
+ * An [HasNextIterator] does not implement the [Iterator] interface.
+ */
+class HasNextIterator<E> {
+  static const int _HAS_NEXT_AND_NEXT_IN_CURRENT = 0;
+  static const int _NO_NEXT = 1;
+  static const int _NOT_MOVED_YET = 2;
+
+  Iterator _iterator;
+  int _state = _NOT_MOVED_YET;
+
+  HasNextIterator(this._iterator);
+
+  bool get hasNext {
+    if (_state == _NOT_MOVED_YET) _move();
+    return _state == _HAS_NEXT_AND_NEXT_IN_CURRENT;
+  }
+
+  E next() {
+    // Call to hasNext is necessary to make sure we are positioned at the first
+    // element when we start iterating.
+    if (!hasNext) throw new StateError("No more elements");
+    assert(_state == _HAS_NEXT_AND_NEXT_IN_CURRENT);
+    E result = _iterator.current;
+    _move();
+    return result;
+  }
+
+  void _move() {
+    if (_iterator.moveNext()) {
+      _state = _HAS_NEXT_AND_NEXT_IN_CURRENT;
+    } else {
+      _state = _NO_NEXT;
+    }
+  }
+}