static void printObjectLayout(O o) {
  if (o instanceof Class) o = nu((Class) o);
  print("Size of object " + className(o) + ": " + unsafe_sizeOf(o) + " bytes");
  for (Pair<S, Long> p : mapPairs(unsafe_allFieldOffsets(o)))
    print("  Field " + p.a + " is at offset " + p.b);
  print();
}