sclass FunctionTimings<A> {
  Map<A, Average> data = syncMap();
  
  void time(A function, Runnable r) {
    if (r == null) ret;
    Average avg = mapGetOrCreate(data, function, -> new Average);
    long time = nanoTime();
    try {
      r.run();
    } finally {
      time = nanoTime()-time;
      avg.add(time);
    }
  }
  
  Map<A, Average> get() { ret cloneMap(data); }
}