Preconditions.checkArgument(!this.keyStrengths.contains(Strength.SOFT));
    return this;
  }

  @CanIgnoreReturnValue
  CacheBuilderFactory withValueStrengths(Set<Strength> valueStrengths) {
    this.valueStrengths = new LinkedHashSet<>(valueStrengths);
    return this;
  }

  Iterable<CacheBuilder<Object, Object>> buildAllPermutations() {
    Iterable<List<Object>> combinations =
        buildCartesianProduct(