*
   * <p><b>Performance note:</b> The returned array has the same full memory footprint as this one
   * does (no actual copying is performed). To reduce memory usage, use {@code subArray(start,
   * end).trimmed()}.
   */
  public ImmutableIntArray subArray(int startIndex, int endIndex) {
    Preconditions.checkPositionIndexes(startIndex, endIndex, length());
    return startIndex == endIndex
        ? EMPTY