The Iterator class provides methods to iterate over an object. It is transparently used by the for-in construct to test for the end of the iteration, and to get the elements.

If the object iterated over is changed during the iteration, the behavior is unspecified.

The Iterator is initially positioned before the first element. Before accessing the first element the iterator must thus be advanced (moveNext) to point to the first element. If there is no element left, then moveNext returns false.

A typical usage of an Iterator looks as follows:

var it = obj.iterator;
while (it.moveNext()) {
  use(it.current);
}

abstract class Iterator<E> {
 /**
  * Moves to the next element. Returns true if [current] contains the next
  * element. Returns false, if no element was left.
  *
  * It is safe to invoke [moveNext] even when the iterator is already
  * positioned after the last element. In this case [moveNext] has no effect.
  */
 bool moveNext();

 /**
  * Returns the current element.
  *
  * Return [:null:] if the iterator has not yet been moved to the first
  * element, or if the iterator has been moved after the last element of the
  * [Iterable].
  */
 E get current;
}