How to extract Left or Right easily from Either type in Dart (Dartz)

Question

I am looking to extract a value easily from a method that return a type Either.

I am doing some tests but unable to test easily th

Answer 1

  Future<Either<Failure, FactsBase>> call(Params params) async {
final resulting = await repository.facts();
return resulting.fold(
  (failure) {
    return Left(failure);
  },
  (factsbase) {
    DateTime cfend = sl<EndDateSetting>().finish;        
    List<CashAction> actions = factsbase.transfers.process(facts: factsbase, startDate: repository.today, finishDate: cfend); // process all the transfers in one line using extensions
    actions.addAll(factsbase.transactions.process(facts: factsbase, startDate: repository.today, finishDate: cfend));
    for(var action in actions) action.account.cashActions.add(action); // copy all the CashActions to the Account.
    for(var account in factsbase.accounts) account.process(start: repository.today);
    return Right(factsbase);
  },
);

}

Answer 2

Ok here the solutions of my problems:

To extract/retrieve the data

final Either<ServerException, TokenModel> result = await repository.getToken(...);
result.fold(
 (exception) => DoWhatYouWantWithException, 
 (tokenModel) => DoWhatYouWantWithModel
);

//Other way to 'extract' the data
if (result.isRight()) {
  final TokenModel tokenModel = result.getOrElse(null);
}

To test the exception

//You can extract it from below, or test it directly with the type
expect(() => result, throwsA(isInstanceOf<ServerException>()));

Answer 3

I can't post a comment... But maybe you could look at this post. It's not the same language, but looks like it's the same behaviour.

Good luck.