* task cannot be implemented with {@link ListeningExecutorService}, the various {@link Futures}
 * utility methods, or {@link ListenableFutureTask}. Those APIs have less opportunity for developer
 * error. If your needs are more complex than {@code SettableFuture} supports, use {@link
 * AbstractFuture}, which offers an extensible version of the API.
 *
 * @author Sven Mawson
 * @since 9.0 (in 1.0 as {@code ValueFuture})
 */
@GwtCompatible

  }

  @Override
  public final void clear() {
    backingMap.clear();
    size = 0;
  }

  /**
   * Skeleton of per-entry iterators. We could push this down and win a few bytes, but it's complex
   * enough it's not especially worth it.
   */
  abstract class Itr<T extends @Nullable Object> implements Iterator<T> {
    int entryIndex = backingMap.firstIndex();
    int toRemove = -1;

 *       MoreExecutors.listeningDecorator}.
 *   <li>If you manually call {@link java.util.concurrent.FutureTask#set} or a similar method,
 *       create a {@link SettableFuture} instead. (If your needs are more complex, you may prefer
 *       {@link AbstractFuture}.)
 * </ul>
 *
 * <p><b>Test doubles</b>: If you need a {@code ListenableFuture} for your test, try a {@link

 *       MoreExecutors.listeningDecorator}.
 *   <li>If you manually call {@link java.util.concurrent.FutureTask#set} or a similar method,
 *       create a {@link SettableFuture} instead. (If your needs are more complex, you may prefer
 *       {@link AbstractFuture}.)
 * </ul>
 *
 * <p><b>Test doubles</b>: If you need a {@code ListenableFuture} for your test, try a {@link