[Union query] What does the r do in the switch-case?

[dontwan]

Hello,

When generating a union query in Artemis, a toJson function is generated. Within this function, there is a switch-case statement. Does anyone know what the r means in case r'Hoge'?

@JsonSerializable(explicitToJson: true)
class Home$Query$HomeResult$HomePayload$HomeItem extends JsonSerializable
    with EquatableMixin {
  Home$Query$HomeResult$HomePayload$HomeItem();

  factory Home$Query$HomeResult$HomePayload$HomeItem.fromJson(
      Map<String, dynamic> json) {
    switch (json['__typename'].toString()) {
      case r'Hoge':
        return Home$Query$HomeResult$HomePayload$HomeItem$Hoge.fromJson(
            json);
      case r'Fuga':
        return Home$Query$HomeResult$HomePayload$HomeItem$Fuga
            .fromJson(json);
      default:
    }
    return _$Home$Query$HomeResult$HomePayload$HomeItemFromJson(json);
  }

  @override
  List<Object?> get props => [];
  @override
  Map<String, dynamic> toJson() {
    switch ($$typename) { // this line it produces error `Undefined name '$$typename'`
      case r'Hoge':
        return (this as Home$Query$HomeResult$HomePayload$HomeItem$Hoge)
            .toJson();
      case r'Fuga':
        return (this
                as Home$Query$HomeResult$HomePayload$HomeItem$Fuga)
            .toJson();
      default:
    }
    return _$Home$Query$HomeResult$HomePayload$HomeItemToJson(this);
  }
}

[vasilich6107]