}

  abstract C combine(List<@Nullable Present<V>> values);

  /** Used for {@link Futures#allAsList} and {@link Futures#successfulAsList}. */
  static final class ListFuture<V extends @Nullable Object>
      extends CollectionFuture<V, List<@Nullable V>> {
    ListFuture(
        ImmutableCollection<? extends ListenableFuture<? extends V>> futures,
        boolean allMustSucceed) {
      super(futures, allMustSucceed);
      init();
    }