@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());
  }

  /**

          .put(Splitter.class, Splitter.on(','))
          .put(com.google.common.base.Optional.class, com.google.common.base.Optional.absent())
          .put(Predicate.class, Predicates.alwaysTrue())
          .put(Equivalence.class, Equivalence.equals())
          .put(Ticker.class, Ticker.systemTicker())
          .put(Stopwatch.class, Stopwatch.createUnstarted())
          // io types

  }

  public void testToImmutableMultiset() {
    BiPredicate<ImmutableMultiset<String>, ImmutableMultiset<String>> equivalence =
        (ms1, ms2) -> ms1.equals(ms2) && ms1.entrySet().asList().equals(ms2.entrySet().asList());
    CollectorTester.of(ImmutableMultiset.<String>toImmutableMultiset(), equivalence)
        .expectCollects(ImmutableMultiset.of())
        .expectCollects(

        toImmutableMap(Entry::getKey, Entry::getValue);
    Equivalence<ImmutableMap<String, Integer>> equivalence =
        Equivalence.equals().<Entry<String, Integer>>pairwise().onResultOf(ImmutableMap::entrySet);
    CollectorTester.of(collector, equivalence)
        .expectCollects(
            ImmutableMap.of("one", 1, "two", 2, "three", 3),
            mapEntry("one", 1),

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

        toImmutableBiMap(Entry::getKey, Entry::getValue);
    Equivalence<ImmutableBiMap<String, Integer>> equivalence =
        Equivalence.equals()
            .<Entry<String, Integer>>pairwise()
            .onResultOf(ImmutableBiMap::entrySet);
    CollectorTester.of(collector, equivalence)
        .expectCollects(
            ImmutableBiMap.of("one", 1, "two", 2, "three", 3),

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

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

    /**
     * Returns the default equivalence strategy used to compare and hash keys or values referenced

  @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<ImmutableSortedSet<String>, ImmutableSortedSet<String>> equivalence =
        Equivalence.equals()
            .onResultOf(ImmutableSortedSet<String>::comparator)
            .and(Equivalence.equals().onResultOf(ImmutableSortedSet::asList))
            .and(Equivalence.equals());
    CollectorTester.of(collector, equivalence)
        .expectCollects(

    MapMakerStrongKeysStrongValues {
      @Override
      public <K extends Comparable<K>, V> Map<K, V> create(Map<K, V> map) {
        // We use a "custom" equivalence to force MapMaker to make a MapMakerInternalMap.
        ConcurrentMap<K, V> newMap = new MapMaker().keyEquivalence(Equivalence.equals()).makeMap();
        checkState(newMap instanceof MapMakerInternalMap);
        newMap.putAll(map);
        return newMap;
      }
    },