docs: def _auto_init(self, *args, **kwrds):
      """Our decorator will add this as __init__ to target classes."""
      for fld in getattr(self, '__fields__', []):
          val = kwrds.get(fld.name, _NO_VAL)
          if val is _NO_VAL:
              val = fld.get_default_val()
          setattr(self, fld.name, val)
  
      if callable(getattr(self, 'setup', None)):
          self.setup(*args, **kwrds)