How to initialize Either Right to an empty value in flutter – Reloaded

November 14, 2022

How do I correctly initialize my Either object in the following code?

class JobListState extends Equatable {
  const JobListState({
    this.status = JobListStatus.initial,
    this.jobListSections = Right([]),
    this.filter,
  });

  final JobListStatus status;
  final Either<Failure, List<JobListViewmodel?>> jobListSections;
  final JobListFilter? filter;

A very similar question was answered 1,5 years ago, but this results in the error The default value of an optional parameter must be constant.

And I guess, if I declare this.jobListSections = const Right([]), I can no longer assign left.

I am assigning the initial value to create the initial state for Bloc.

>Solution :

Because your variables are final you can not change it directly. You can declare copyWith method to change your values.

class JobListState extends Equatable {
  const JobListState({
    this.status = JobListStatus.initial,
    this.jobListSections = Right([]),
    this.filter,
  });

  final JobListStatus status;
  final Either<Failure, List<JobListViewmodel?>> jobListSections;
  final JobListFilter? filter;

  JobListState copyWith({
    JobListStatus? status,
    Either<Failure, List<JobListViewmodel?>>? jobListSections,
    JobListFilter? filter
  }) {
     return JobListState(
       status: status ?? this.status,
       jobListSections: jobListSections ?? this.jobListSections,
       filter: filter ?? this.filter
     );
  }
}

// anywhere you use JobListState
var state = JobListState(); // state.jobListSections is Right([])
state = state.copyWith(jobListSections: Left(Failure())); // state.jobListSections is Left
// here you have new state that you can emit it.