sclass HashedBWImage is MakesBufferedImage {
  BWImage image; // don't change this afterwards...
  long hash;
  
  *(BWImage *image) { assertNotNull(image); }
  
  long hash() {
    if (hash == 0) {
      hash = hashBWImage(image);
      if (hash == 0) reportHashCollision(this);
    }
    ret hash;
  }
  
  equals HashedBWImage o {
    if (hash() != o.hash()) false;
    if (!bwImagesIdentical(image, o.image)) {
      reportHashCollision(this, o);
      false;
    }
    true;
  }
  
  public int hashCode() { ret (int) hash; }
  
  BWImage get() { ret image; }
  
  public int getWidth() { ret image.getWidth(); }
  public int getHeight() { ret image.getHeight(); }
  public BufferedImage getImage() { ret image.getBufferedImage(); }
}