code: func (model *Model) WriteTo(w io.Writer) (int64, error) {
  	model.RLock()
  	defer model.RUnlock()
  	b, err := json.Marshal(model)
  	if err != nil {
  		return 0, err
  	}
  	n, err := w.Write(b)
  	if err != nil {
  		return int64(n), err
  	}
  	return int64(n), nil
  }
docs: // WriteTo writes a model to a Writer