code: func (e Enum) GetKey(value interface{}) string {
  	for k, v := range e {
  		if reflect.DeepEqual(v, value) {
  			return k
  		}
  	}
  	return ""
  }
docs: // GetKey performs reverse lookup of the enumeration value, returning the
  // key that corresponds to the value.
  //
  // If multiple keys correspond to the same value, the result is undefined.