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