!7

// not tested on null values
sclass FieldIndex<A extends Concept, Val> implements IConceptIndex {
  //Concepts concepts;
  Class<A> cc;
  S field;
  new HashMap<Concept, O> objectToValue;
  new MultiMap<O, Concept> valueToObject;
  
  *() {}
  *(Concepts concepts, Class<A> *cc, S *field) {
    concepts.conceptIndices.add(this);
    for (A c : list(concepts, cc))
      update(c);
  }
  
  public synchronized void update(Concept c) {
    O newValue = cget(c, field);
    O oldValue = objectToValue.get(c);
    if (newValue != oldValue) {
      valueToObject.remove(oldValue, c);
      valueToObject.add(newValue, c);
      objectToValue.put(c, value);
    }
  }
  
  public synchronized void remove(Concept c) {
    O value = cget(c, field);
    objectToValue.remove(c);
    valueToObject.remove(value, c);
  }
  
  synchronized A get(Val value) {
    ret first(valuesToObject.get(value));
  }
  
  synchronized L<A> getAll(Val value) {
    ret valuesToObject.get(value);
  }
}

concept CC {
  S a, b;
}

p {
  nu(CC, a := "hello", b := "world");
  FieldIndex<CC, S> index = new(mainConcepts, CC, "a");
  assertEquals("world", index.get("hello").b);
  assertNull(index.get("Hello"));
  print("OK");
}