* implementation types do not leak into the serialized representation.
   */
  @J2ktIncompatible // serialization
  static final class SerializedForm implements Serializable {
    final Object[] elements;

    SerializedForm(Object[] elements) {
      this.elements = elements;
    }

    Object readResolve() {
      return copyOf(elements);
    }

   * particular implementation type is an implementation detail.
   */
  @J2ktIncompatible // serialization
  private static final class SerializedForm implements Serializable {
    final Object[] elements;

    SerializedForm(Object[] elements) {
      this.elements = elements;
    }

    Object readResolve() {
      return copyOf(elements);
    }