code: func toString(val interface{}) string {
  	switch actual := val.(type) {
  	case string:
  		return actual
  	case int:
  		return strconv.Itoa(actual)
  	case float64:
  		return strconv.FormatFloat(actual, 'f', -1, 64)
  	case bool:
  		return strconv.FormatBool(actual)
  	default:
  		panic("unexpected key type")
  	}
  }
docs: // toString returns the string representation of the given type.