sclass CalculatedConceptFieldIndex<A extends Concept, Val> implements IConceptIndex {
  Class<A> cc;
  IF1<A, Val> f;
  new HashMap<A, Val> objectToValue;
  new MultiMap<Val, A> valueToObject;
  
  *() {}
  *(Class<A> cc, IF1<A, Val> f) { this(db_mainConcepts(), cc, f); }
  
  *(Concepts concepts, Class<A> *cc, IF1<A, Val> *f) {
    concepts.addConceptIndex(this);
    for (A c : list(concepts, cc))
      updateImpl(c);
  }
  
  public void update(Concept c) {
    if (!isInstance(cc, c)) ret;
    updateImpl((A) c);
  }
  
  synchronized void updateImpl(A c) {
    Val newValue = callF(f, c);
    Val oldValue = objectToValue.get(c);
    if (neq(newValue, oldValue)) {
      valueToObject.remove(oldValue, (A) c);
      valueToObject.put(newValue, (A) c);
      objectToValue.put((A) c, newValue);
    }
  }
  
  public synchronized void remove(Concept c) {
    if (!isInstance(cc, c)) ret;
    Val value = callF(f, (A) c);
    objectToValue.remove(c);
    valueToObject.remove(value, (A) c);
  }
  
  synchronized A get(Val value) {
    ret valueToObject.getFirst(value);
  }
  
  public synchronized L<A> getAll(Val value) {
    ret valueToObject.get(value);
  }
}

Began life as a copy of #1014416