Super-powered enums similar to sealed classes in Kotlin

Installation

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

dependencies:
  super_enum: ^[version]

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

Example

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";

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

  @object
  Error,
}

@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

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

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

  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);
    }
  }

  @override
  List get props => null;
}

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

  final T data;

  final String message;

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

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

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

  static Error _instance;
}

Usage

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
_resultController.add(Result.success(
              data: 333,
              message: 'Success',
            )),

// Adding an error state to the stream controller
_resultController.add(Result.error()),

// Listening to all the possible Result states
_resultController.stream.listen((result) {
      result.when(
        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.

For help getting started with Flutter, view our online documentation, which offers tutorials, samples, guidance on mobile development, and a full API reference.