code: func mutateTimersList(blob *[]byte, cb func(*[]*internal.Timer)) error {
  	list, err := unmarshalTimersList(*blob)
  	if err != nil {
  		return err
  	}
  	cb(&list)
  	*blob = marshalTimersList(list)
  	return nil
  }
docs: // mutateTimersList deserializes the list, calls a callback, which modifies
  // the list and serializes it back.