* Equivalence<? super T> below, no type could satisfy both that bound and T's own
     * bound. With this type, they have some overlap: in our example, Equivalence<Number>
     * and Equivalence<Object>.
     */
    private final Equivalence<? super @NonNull T> equivalence;

    @ParametricNullness private final T reference;

     * Equivalence<? super T> below, no type could satisfy both that bound and T's own
     * bound. With this type, they have some overlap: in our example, Equivalence<Number>
     * and Equivalence<Object>.
     */
    private final Equivalence<? super @NonNull T> equivalence;

    @ParametricNullness private final T reference;

  // actually implement BiPredicate, and CollectorTests expects a BiPredicate.
  static <C, E extends @Nullable Object, R extends Iterable<E>>
      BiPredicate<C, C> pairwiseOnResultOf(Function<C, R> arg) {
    Equivalence<C> equivalence = Equivalence.equals().<E>pairwise().onResultOf(arg);
    return equivalence::equivalent;
  }

   * #weakKeys} is specified, and {@link Equivalence#equals()} otherwise. The only place this is
   * used is in {@link Interners.WeakInterner}.
   */
  @CanIgnoreReturnValue
  @GwtIncompatible // To be supported
  MapMaker keyEquivalence(Equivalence<Object> equivalence) {
    checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);

  }

  public void testToImmutableSet() {
    Collector<String, ?, ImmutableSet<String>> collector = ImmutableSet.toImmutableSet();
    Equivalence<ImmutableSet<String>> equivalence =
        Equivalence.equals().onResultOf(ImmutableSet::asList);
    CollectorTester.of(collector, equivalence)
        .expectCollects(ImmutableSet.of("a", "b", "c", "d"), "a", "b", "a", "c", "b", "b", "d");
  }

  @CanIgnoreReturnValue
  CacheBuilder<K, V> keyEquivalence(Equivalence<Object> equivalence) {
    checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);
    keyEquivalence = checkNotNull(equivalence);
    return this;
  }

  Equivalence<Object> getKeyEquivalence() {
    return MoreObjects.firstNonNull(keyEquivalence, getKeyStrength().defaultEquivalence());
  }

  /**

    BiPredicate<ImmutableSetMultimap<?, ?>, ImmutableSetMultimap<?, ?>> equivalence =
        Equivalence.equals()
            .onResultOf(
                (ImmutableSetMultimap<?, ?> mm) ->
                    ImmutableListMultimap.copyOf(mm).asMap().entrySet().asList())
            .and(Equivalence.equals());
    CollectorTester.of(collector, equivalence)
        .expectCollects(ImmutableSetMultimap.of())
        .expectCollects(

     */

    STRONG {
      @Override
      Equivalence<Object> defaultEquivalence() {
        return Equivalence.equals();
      }
    },

    SOFT {
      @Override
      Equivalence<Object> defaultEquivalence() {
        return Equivalence.identity();
      }
    },

    WEAK {
      @Override
      Equivalence<Object> defaultEquivalence() {
        return Equivalence.identity();

    BiPredicate<ImmutableListMultimap<?, ?>, ImmutableListMultimap<?, ?>> equivalence =
        Equivalence.equals()
            .onResultOf((ImmutableListMultimap<?, ?> mm) -> mm.asMap().entrySet().asList())
            .and(Equivalence.equals());
    CollectorTester.of(collector, equivalence)
        .expectCollects(ImmutableListMultimap.of())
        .expectCollects(

    BiPredicate<ImmutableSortedMap<String, Integer>, ImmutableSortedMap<String, Integer>>
        equivalence =
            Equivalence.equals()
                .onResultOf(ImmutableSortedMap<String, Integer>::comparator)
                .and(Equivalence.equals().onResultOf(map -> map.entrySet().asList()))
                .and(Equivalence.equals());
    ImmutableSortedMap<String, Integer> expected =