static <A> A highestByFunction(Iterable<A> l, O f) {
  A best = null;
  O bestValue = null;
  if (l != null) for (A a : l) {
    O val = callF(f, a);
    if (best == null || cmp(val, bestValue) > 0) {
      best = a;
      bestValue = val;
    }
  }
  ret best;
}