code: func (sf singleFeature) GobEncode() ([]byte, error) {
  	var buf bytes.Buffer
  	encoder := gob.NewEncoder(&buf)
  
  	if err := encoder.Encode(sf.featureType); err != nil {
  		return nil, err
  	}
  
  	if err := encoder.Encode(sf.value); err != nil {
  		return nil, err
  	}
  
  	return buf.Bytes(), nil
  }
docs: /* Feature Gob interface */