}
    return (ListenableFuture<? extends T>[]) collection.toArray(new ListenableFuture<?>[0]);
  }

  // This can't be a TrustedFuture, because TrustedFuture has clever optimizations that
  // mean cancel won't be called if this Future is passed into setFuture, and then
  // cancelled.
  private static final class InCompletionOrderFuture<T extends @Nullable Object>
      extends AbstractFuture<T> {

   * syntax</a>. One caveat to this is that the {@code TreeSet} constructor uses a null {@code
   * Comparator} to mean "natural ordering," whereas this factory rejects null. Clean your code
   * accordingly.
   *
   * @param comparator the comparator to use to sort the set
   * @return a new, empty {@code TreeSet}

 * Implementations are strongly encouraged to be side-effect-free and immutable.
 *
 * <p>Throughout the documentation of this class, the phrase "matching character" is used to mean
 * "any {@code char} value {@code c} for which {@code this.matches(c)} returns {@code true}".
 *
 * <p><b>Warning:</b> This class deals only with {@code char} values, that is, <a