// quadratic cost of adding them to the COWAS directly.
    Collection<? extends E> elementsCollection =
        (elements instanceof Collection)
            ? (Collection<? extends E>) elements
            : Lists.newArrayList(elements);
    return new CopyOnWriteArraySet<>(elementsCollection);
  }

  /**
   * Creates an {@code EnumSet} consisting of all enum values that are not in the specified