dart Either

either.dart

abstract class IGlobalFailure implements Exception {
  final String? message;
  IGlobalFailure({this.message});
}

abstract class EitherFailure implements Exception {
  final String? message;
  EitherFailure({this.message});
}

class ResponseNotDefinedFailure extends EitherFailure {
  ResponseNotDefinedFailure()
      : super(message: 'Invalid Response. Failure or Success not defined');
}

abstract class Either<TSuccess, TFailure> {
  final TFailure? _failure;
  final TSuccess? _success;
  Either({TSuccess? success, TFailure? failure})
      : _failure = failure,
        _success = success,
        assert(success != null || failure != null)
  //assert(failure == null && success != null)
  ;

  T fold<T>(T Function(TFailure)? onFailure, T Function(TSuccess)? onSuccess) {
    if (_failure != null && onFailure != null) return onFailure(_failure!);
    if (_success != null && onSuccess != null) return onSuccess(_success!);
    throw ResponseNotDefinedFailure();
  }

  static Right<TSuccess, TFailure> success<TSuccess, TFailure>(
          TSuccess value) =>
      Right<TSuccess, TFailure>(value);

  static Left<TSuccess, TFailure> failure<TSuccess, TFailure>(TFailure value) =>
      Left<TSuccess, TFailure>(value);

  bool get isSuccess => _success != null;
  bool get isFailure => _failure != null;

  // ignore: unnecessary_this
  TSuccess? operator |(TSuccess? newFailureResponse) =>
      this.fold((_) => newFailureResponse, (value) => value);
}

class Right<TSuccess, TFailure> extends Either<TSuccess, TFailure> {
  Right(TSuccess value) : super(success: value);
}

class Left<TSuccess, TFailure> extends Either<TSuccess, TFailure> {
  Left(TFailure value) : super(failure: value);
}