* stable. There is usually no reason to retain a reference of type {@code SetView}; typically,
   * you either use it as a plain {@link Set}, or immediately invoke {@link #immutableCopy} or
   * {@link #copyInto} and forget the {@code SetView} itself.
   *
   * @since 2.0
   */
  public abstract static class SetView<E extends @Nullable Object> extends AbstractSet<E> {
    private SetView() {} // no subclasses but our own

    /**
     * 
     */
    void clearAttributeCache () {
        this.attrExpiration = 0;
        this.sizeExpiration = 0;
    }


    @Override
    public void copyTo ( SmbResource d ) throws SmbException {
        if ( ! ( d instanceof SmbFile ) ) {
            throw new SmbException("Invalid target resource");
        }
        SmbFile dest = (SmbFile) d;