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Super-powered enums similar to sealed classes in Kotlin


Add the following to you pubspec.yaml and replace [version] with the latest version:

  super_enum: ^[version]

  super_enum_generator: ^[version]
  build_runner: ^1.7.1 // Any latest version which works with your current Dart or Flutter SDK


A Super Enum can be easily generated by annotating a private enum with @superEnum

import 'package:super_enum/super_enum.dart';

part "result.g.dart";

enum _Result {
  @Data(fields: [
    DataField('data', Generic),
    DataField('message', String),


@Data() marks an enum value to be treated as a Data class.

  • One should supply a list of possible fields inside the annotation.
  • If you don't want to add fields, use @object annotation instead.
  • Fields are supplied in the form of DataField objects.
  • Each DataField must contain the name and the type of the field.
  • If the field type needs to be generic use Generic type and annotate the enum value with @generic annotation.

@object marks an enum value to be treated as an object.

Run the build_runner command to generate the filename.g.dart part file.

 # Dart SDK: $pub run build_runner build
 # Flutter SDK: $flutter pub run build_runner build

Generated file

abstract class Result<T> extends Equatable {
  const Result(this._type);

  factory Result.success({@required T data, @required String message}) =

  factory Result.error() = Error<T>;

  final _Result _type;

//ignore: missing_return
  R when<R>(
      {@required R Function(Success) success,
      @required R Function(Error) error}) {
    switch (this._type) {
      case _Result.Success:
        return success(this as Success);
      case _Result.Error:
        return error(this as Error);

  List get props => null;

class Success<T> extends Result<T> {
  const Success({@required this.data, @required this.message})
      : super(_Result.Success);

  final T data;

  final String message;

  String toString() => 'Success(data:${this.data},message:${this.message})';
  List get props => [data, message];

class Error<T> extends Result<T> {
  const Error._() : super(_Result.Error);

  factory Error() {
    _instance ??= Error._();
    return _instance;

  static Error _instance;


Below is just one of the use-case of Super Enums. It can be used wherever you want to manage state.

// Creating an StreamController of type Result<int>
final _resultController = StreamController<Result<int>>();

// Adding a success state to the stream controller
              data: 333,
              message: 'Success',

// Adding an error state to the stream controller

// Listening to all the possible Result states
_resultController.stream.listen((result) {
        onSuccess: (data) => print(data.message), // Success
        onError: (_) => print('Error Occured'), // Error Occured

Getting Started

This project is a starting point for a Dart package, a library module containing code that can be shared easily across multiple Flutter or Dart projects.

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