* iterates. This class is not thread safe.
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class ConsumingQueueIterator<T extends @Nullable Object> extends AbstractIterator<T> {
  private final Queue<T> queue;

  ConsumingQueueIterator(Queue<T> queue) {
    this.queue = checkNotNull(queue);
  }

  @Override
  @CheckForNull
  protected T computeNext() {

    checkNotNull(iterable);

    return new FluentIterable<T>() {
      @Override
      public Iterator<T> iterator() {
        return (iterable instanceof Queue)
            ? new ConsumingQueueIterator<>((Queue<T>) iterable)
            : Iterators.consumingIterator(iterable.iterator());
      }

      @Override
      public String toString() {
        return "Iterables.consumingIterable(...)";

   * this method will write nulls into the array during iteration.
   *
   * <p>This is mainly just to avoid the intermediate ArrayDeque in ConsumingQueueIterator.
   */
  private static <I extends Iterator<?>> Iterator<I> consumingForArray(@Nullable I... elements) {
    return new UnmodifiableIterator<I>() {
      int index = 0;

      @Override