// A is the user object associated with each mask (aka a "label")

sclass G22HashedMasks<A> {

  record noeq Mask(Image2B image, A label) is IG22Mask<A> {

    int hash, count;

    public int hashCode() {

      if (hash == 0)

        hash = (int) hashImage2B(image);

      ret hash;

    }

    public Image2B image() { ret image; }

    public A label() { ret label; }

  }

  new Map<Int, Mask> masks;

  void addRegion(IImageRegion region, A label) {

    var mask = new Mask(regionToMaskImage(region), label);

    var existingMask = masks.get(mask.hashCode());

    if (existingMask != null) {

      labels.remove(existingMask.label);

      existingMask.label = combineLabels(existingMask.label, mask.label);

      mask = existingMask;

    } else

      masks.put(mask.hashCode(), mask);

    ghost_cache = null;

    certainty_cache = null;

    labels.add(mask.label);

    mask.count++;

  }

  swappable A combineLabels(A a, A b) {

    if (a == null) ret b;

    if (b == null) ret a;

    if (eq(a, b)) ret a;

    fail("Label conflict: " + a + " / " + b);

  }

  L<Mask> masks() { ret valuesList(masks); }

  !include early #1035854 // Masks holder Include

}