sclass FieldAsVar<A> extends VarWithNotify<A> {
  IHasChangeListeners containingObject;
  S fieldName;
  IF0<A> getter;
  IVF1<A> setter;

  *(IHasChangeListeners *containingObject,
    S *fieldName, IF0<A> *getter, IVF1<A> *setter) {
    containingObject.onChange(l0 _updateFromObject);
  }
  
  void _updateFromObject {
    set(getter!);
  }
  
  void fireChange {
    super.fireChange();
    setter.set(get());
  }
}