With dartz is it possible to pass a failure on to the function that is folding my either - flutter

Question

I have the following code
class GetAuthUserUseCase {
final AuthRepository _authRepository;
GetAuthUserUseCase({
required AuthRepository authRepository,
}) : _authRepository = authRepository;
Future<Either<Failure, AuthUser>> call() async {
final userResponse = await _authRepository.getUser();
var user = userResponse.fold(
(Failure l) => //How can I return the failure from the call function?,
(AuthUser r) => r,
);
final accessTokenExpiresAtMilliseconds =
user.accessTokenIssuedAtMilliseconds + user.accessTokenExpiresInMilliseconds;
final accessTokenExpiresAtDateTime =
DateTime.fromMillisecondsSinceEpoch(accessTokenExpiresAtMilliseconds);
if (DateTime.now().isBefore(accessTokenExpiresAtDateTime)) {
return userResponse;
}
return _authRepository.refreshUser(
user: user,
);
}
}
In my use case I have some business logic to determines whether I need to refresh a users access token or not. Based on that I refresh my user. But I need to load my user first with getUser() in order to determine if the access token has expired.
The getUser() will return an Either<Failure,AuthUser> so I fold that to get the user. But what I want is tho propagate the failure so it terminates the call method and outputs that failure from the call method.
I would like to avoid doing a type check for Failure or AuthUser if possible since I think it will make my program less robust.
Is this possible?

Answer 1

For this case, you can use isLeft() to check the failure. and isRight() on success.
Future<Either<Failure, AuthUser>> call() async {
final userResponse = await _authRepository.getUser();
if(userResponse.isLeft()){
// do your stuffs
}
Inside this, you may like to access data directly, this extension will help
extension EitherX<L, R> on Either<L, R> {
R asRight() => (this as Right).value; //
L asLeft() => (this as Left).value;
}