static <A, B> Pair<B, Bool> syncGetOrCreate2(Map<A, B> map, A key, Class<? extends B> c) ctex {
  synchronized(map) {
    B b = map.get(key);
    if (b == null) {
      map.put(key, b = c.newInstance());
      ret pair(b, true);
    }
    ret pair(b, false);
  }
}

// TODO: syntax with function