@Override
  public Set<Entry<K, V>> entrySet() {
    // does not impact recency ordering
    Set<Entry<K, V>> es = entrySet;
    return (es != null) ? es : (entrySet = new EntrySet(this));
  }

  /**
   * Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying
   * map.
   */
  private final class WriteThroughEntry implements Entry<K, V> {
    final K key;
    V value;