static L<S> getFieldOrder(O o) {
  //S s = cast callOpt(o, "_fieldOrder");
  //if (s != null) ret splitAtSpace(s);
  ret getFieldOrder(_getClass(o));
}

static L<S> getFieldOrder(Class c) {
  if (c == null) null;
  ret splitAtSpace(toStringOpt(getOpt(c, '_fieldOrder)));
}