private int storeClass(EqClassImpl eqClass) {
    int freeIndex = myEqClasses.indexOf(null);
    int resultIndex = freeIndex >= 0 ? freeIndex : myEqClasses.size();
    if (freeIndex >= 0) {
      myEqClasses.set(freeIndex, eqClass);
    }
    else {
      myEqClasses.add(eqClass);
    }
    eqClass.forValues(id -> myIdToEqClassesIndices.put(id, resultIndex));
    return resultIndex;
  }
private int storeClass(EqClassImpl eqClass)