Flutter Either fold is skipped - flutter

Question

I'm working on a small app with GoogleSignIn-Auth. and stumbled upon a bug I cannot wrap my head around.
It seems like the fold of an Either seems to be skipped. It used to work before, when I had a complicated pile of blocs. Since I started reorganizing my widgets it started to this.
Future<Either<Failure, SignUpSuccess>> signInWithGoogle() async {
try {
final signUpSuccess = await googleRemoteDataSource.signInWithGoogle();
signUpSuccess.fold(
(failure) => () {
print("Got failure!");
return Left(GeneralFailure());
},
(success) => () {
return Right(signUpSuccess);
});
print("I skipped the fold!");
} catch (e) {
print("Caught exception!");
return Left(GeneralFailure());
}
print("Instant fail!");
return Left(GeneralFailure());
}
I have a widget that's listening to a SignInBloc emitting the states:
class SignUpRoot extends StatelessWidget {
SignUpRoot({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
body: BlocProvider(
create: (context) => sl<SignInBloc>(),
child: BlocListener<SignInBloc, SignInState>(
listener: (context, state) {
if (state is SignInWithGoogleLoaded) {
// Navigate to SignInNamePage
print("This seems to work!");
} else if (state is SignInWithGoogleLoading) {
// Navigate to loading page
print("Loading Google...");
} else if (state is SignInError) {
// Navigate to error page
print("An error occured while signing in!");
}
},
child: const SignUpMainPage(),
)));
}
And last but not least my bloc:
class SignInBloc extends Bloc<SignInEvent, SignInState> {
final SignUpUseCases useCases;
SignInBloc({required this.useCases}) : super(SignInInitial()) {
on<SignInWithGooglePressed>((event, emit) async {
// Show Loading indicator
emit(SignInWithGoogleLoading());
// wait for sign in response
Either<Failure, SignUpSuccess> successOrFailure =
await useCases.signInWithGoogle();
// emit corresponding state
successOrFailure.fold(
(failure) => emit(SignInError()),
(success) => () {
// emit sign in loaded state
emit(SignInWithGoogleLoaded());
// create new (local) user
// assign user data e.g. display name
});
});
}
}
Thanks for any help!

Answer 1

The problem is that the fold method returns the value of the left or right functions.
https://pub.dev/documentation/dartz/latest/dartz/Either/fold.html
B fold<B>(
B ifLeft(
L l
),
B ifRight(
R r
)
)
Your code should be corrected to:
Future<Either<Failure, SignUpSuccess>> signInWithGoogle() async {
try {
final signUpSuccess = await googleRemoteDataSource.signInWithGoogle();
return signUpSuccess.fold(
(failure) => () {
return Left(GeneralFailure());
},
(success) => () {
return Right(signUpSuccess);
});
} catch (e) {
return Left(GeneralFailure());
}
return Left(GeneralFailure());
}
I just added the return at the start of the fold, now the value returned from left or right will be returned by your function.

Answer 2

You just have to remove the arrow in the success part of the fold.
Future<Either<Failure, SignUpSuccess>> signInWithGoogle() async {
try {
final signUpSuccess = await googleRemoteDataSource.signInWithGoogle();
signUpSuccess.fold(
(failure) => () {
print("Got failure!");
return Left(GeneralFailure());
},
(success){
return Right(signUpSuccess);
});
print("I skipped the fold!");
} catch (e) {
print("Caught exception!");
return Left(GeneralFailure());
}
print("Instant fail!");
return Left(GeneralFailure());
}
class SignInBloc extends Bloc<SignInEvent, SignInState> {
final SignUpUseCases useCases;
SignInBloc({required this.useCases}) : super(SignInInitial()) {
on<SignInWithGooglePressed>((event, emit) async {
// Show Loading indicator
emit(SignInWithGoogleLoading());
// wait for sign in response
Either<Failure, SignUpSuccess> successOrFailure =
await useCases.signInWithGoogle();
// emit corresponding state
successOrFailure.fold(
(failure) => emit(SignInError()),
(success) {
emit(SignInWithGoogleLoaded());
});
});
}
}