concept Entity > NamedConcept {
}

abstract concept AbstractJavaObjectEntity<A> > Entity {
  abstract A object();
  
  toString {
    S s = super.toString();
    O o = object();
    if (o != null)
      s += " " + str_pcall(o);
    ret s;
  }
}

concept TransientJavaObjectEntity<A> > AbstractJavaObjectEntity<A> {
  gettable transient A object;
}

concept PersistentJavaObjectEntity<A> > AbstractJavaObjectEntity<A> {
  gettable A object;
}

concept ConceptEntity<A extends Concept> extends AbstractJavaObjectEntity<A> {
  new Ref<A> concept;
  
  *(A concept) { this.concept.set(concept); }
  
  A object() { ret concept!; }
}