// value is true or false (persistent/transient)
// but may be extended in the future
svoid addToPersistenceInfo(O o, S field, O value) {
  synchronized(o) {
    Map pi = getOpt _persistenceInfo(o);
    if (pi == null)
      setOpt(o, _persistenceInfo := pi = new LinkedHashMap);
    else
      syncMapPut(_persistenceInfo, field, value);
  }
}