* @since 3.0
   */
  public static <E> ImmutableSet<E> copyOf(E[] elements) {
    return fromArrayWithExpectedSize(elements, estimatedSizeForUnknownDuplication(elements.length));
  }

  private static <E> ImmutableSet<E> fromArrayWithExpectedSize(E[] elements, int expectedSize) {
    switch (elements.length) {
      case 0:
        return of();
      case 1: