sclass Lowest<A> {
  A best;
  double score;
  transient O onChange;
  
  bool isNewBest(double score) {
    ret best == null || score < this.score;
  }
  
  double bestScore() {
    ret best == null ? Double.NaN : score;
  }
  
  float floatScore() {
    ret best == null ? Float.NaN : (float) score;
  }
  
  bool put(A a, double score) {
    if (a != null && isNewBest(score)) {
      best = a;
      this.score = score;
      pcallF(onChange);
      ret true;
    }
    ret false;
  }
  
  A get() { ret best; }
  bool has() { ret best != null; }
}