sclass FunctionTimings<A> {
  Map<A, Average> data = syncMap();
  
  void time(A function, Runnable r) {
    if (r == null) ret;
    Average avg = syncMapGetOrCreate(data, function, -> new Average);
    long time = nanoTime();
    try {
      r.run();
    } finally {
      time = nanoTime()-time;
      avg.add(time);
    }
  }
  
  Map<A, Average> get() { ret cloneMap(data); }
  
  void reset aka clear() { data.clear(); }
  
  // as multi-line string, sorted alphabetically
  S render() {
    ret lines(ciSorted(map(get(), (f, avg) ->
      firstToUpper(f) + ": " + n2(iround(nsToMicroseconds(avg!)))
        + " " + microSymbol() + "s (" + n2(iround(avg.n())) + ")")));
  }
}