sclass guessDeepObjectSize_recursive_Data {
  long size;
  Set stack = identityHashSet();
  Set seen = identityHashSet();
}

static long guessDeepObjectSize_recursive(O o) {
  new guessDeepObjectSize_recursive_Data data;
  data.stack.add(o);
  while (nempty(data.stack))
    guessDeepObjectSize_recursive_step(data, popFirst(data.stack));
  ret data.size;
}

svoid guessDeepObjectSize_recursive_step(guessDeepObjectSize_recursive_Data data, O o) {
  if (o == null) ret;
  if (!data.seen.add(o)) ret;
  if (o instanceof Class) ret;
  
  /*if (o cast S) ret with data.size += guessStringSize(o);
  if (o cast ArrayList) {
    data.stack.addAll(o);
  }*/
  
  if (isArray(o)) {
    ret; // TODO
  }
  
  data.size += unsafe_sizeOf(o);
  for (Field f : allFieldObjects(o)) pcall-short {
    O x = f.get(o);
    if (x != null && !data.seen.contains(x)) data.stack.add(x);
  }

  //fail("can't handle object type: " + className(o));
}