return (ks != null) ? ks : (keySet = new KeySet());
  }

  @LazyInit transient @Nullable Collection<V> values;

  @Override
  public Collection<V> values() {
    Collection<V> vs = values;
    return (vs != null) ? vs : (values = new Values());
  }

  @LazyInit transient @Nullable Set<Entry<K, V>> entrySet;

  @Override
  public Set<Entry<K, V>> entrySet() {
    Set<Entry<K, V>> es = entrySet;

     * concurrently, returning once any connection connects successfully.
     *
     * This implements Happy Eyeballs ([RFC 6555][rfc_6555]), balancing connect latency vs.
     * wasted resources.
     *
     * Defaults to enabled, call with [fastFallback] = false to revert to 4.x behaviour.
     *
     * [rfc_6555]: https://datatracker.ietf.org/doc/html/rfc6555
     */