sS standard_toString(O o) {
  if (o == null) ret "null";
  S name = shortClassName(o);
  Set<S> fields = fieldNames(o);
  if (empty(fields)) ret name;
  ret name + "(" + joinWithComma(mapNonNulls(fields, field -> {
    O value = get(o, field);
    if (value == null) null;
    ret field + "=" + str(value);
  })) + ")";
}