@VisibleForTesting final MapMakerInternalMap<E, Dummy, ?, ?> map;

    private InternerImpl(MapMaker mapMaker) {
      this.map =
          MapMakerInternalMap.createWithDummyValues(mapMaker.keyEquivalence(Equivalence.equals()));
    }

    @Override
    public E intern(E sample) {
      while (true) {
        // trying to read the canonical...

    @VisibleForTesting final MapMakerInternalMap<E, Dummy, ?, ?> map;

    private InternerImpl(MapMaker mapMaker) {
      this.map =
          MapMakerInternalMap.createWithDummyValues(mapMaker.keyEquivalence(Equivalence.equals()));
    }

    @Override
    public E intern(E sample) {
      while (true) {
        // trying to read the canonical...

  }

  /**
   * A dummy singleton value type used by {@link Interners}.
   *
   * <p>{@link MapMakerInternalMap} can optimize for memory usage in this case; see {@link
   * MapMakerInternalMap#createWithDummyValues}.
   */
  enum Dummy {
    VALUE
  }

  MapMaker setValueStrength(Strength strength) {
    checkState(valueStrength == null, "Value strength was already set to %s", valueStrength);

   * since a map of dummy values is the exact use case there.
   */
  static <K>
      MapMakerInternalMap<K, Dummy, ? extends InternalEntry<K, Dummy, ?>, ?> createWithDummyValues(
          MapMaker builder) {
    if (builder.getKeyStrength() == Strength.STRONG
        && builder.getValueStrength() == Strength.STRONG) {