code: func (r *RandomID) ModelID() string {
  	if r.ID == "" {
  		r.ID = generateRandomID()
  	}
  	return r.ID
  }
docs: // ModelID returns the id of the model, satisfying the Model interface.
  // If r.ID is an empty string, it will generate a pseudo-random id which
  // is highly likely to be unique.