code: func (i *Index) Close() error {
  	i.mu.Lock()
  	defer i.mu.Unlock()
  
  	// Close the attribute store.
  	i.columnAttrs.Close()
  
  	// Close all fields.
  	for _, f := range i.fields {
  		if err := f.Close(); err != nil {
  			return errors.Wrap(err, "closing field")
  		}
  	}
  	i.fields = make(map[string]*Field)
  
  	return nil
  }
docs: // Close closes the index and its fields.