public boolean isUseReferenceEquality() {
    if (isAnnotationType()) {
      return false;
    }
    return isUseStrongInterned()
        || isUseSingletonOnly()
        || useAttributelessSingleton()
        || isGenerateOrdinalValue();
  }
Means object hashcode is cached at some point. Either lazily (on first access)
or eagerly (during construction).
@see #isUseLazyhash()
@see #isUsePrehashed()
value-processor/src/org/immutables/value/processor/meta/ValueType.java