persistable sclass TargetAndActual<A> extends MetaWithChangeListeners {
  settableWithVar A target;
  settableWithVar A actual;
  
  *(A *target, A *actual) {}
  *(A *target) {}
  
  toString {
    ret commaCombine(
      target == null ?: "Target: " + target,
      actual == null ?: "Actual: " + actual);
  }
  
  A value aka get() { ret actual; }
  
  bool hasTarget() { ret target != null; }
  
  void set aka value(A actual) { actual(actual); }
}