Hi! Any ideas why this doesn't compile? Hope it's fine to put rx code here. It's a lang question. ``...

# announcements

[iex]

Hi! Any ideas why this doesn't compile? Hope it's fine to put rx code here. It's a lang question.

fun foo(): Observable<Result<String, String>> =
    Observable.just(Success(""))
        .onErrorResumeNext { t: Throwable -> Failure("") } // Type mismatch: inferred type is Observable<Result.Success<String>!>! but Observable<Result<String, String>> was expected

// where:

sealed class Result<out T, out E> {
    data class Success<out T>(val success: T) : Result<T, Nothing>()
    data class Failure<out E>(val error: E) : Result<Nothing, E>()
}

[diesieben07]

Observable.just(Success("")) is inferred to be of type Observable<Result.Success<String>>. Your onErrorResumeNext then tries to put a Result.Failure<String> into that, which is not compatible.

[diesieben07]

You either have to specify the type explicitly when calling just or create factory methods for Success and Failure which return Result<T, E> instead of Result.Success / Result.Failure

[iex]

if I try the first:

fun foo(): Observable<Result<String, String>> =
    Observable.just<Result<String, String>>(Success(""))
        .onErrorResumeNext { t: Throwable -> Failure("") }

I get a new error on Failure("")

Expected type mismatch: inferred type is Result.Failure<String> but ObservableSource<out Result<String, String>!>! was expected

🤔

[iex]

ok, how do I specify that the later returns also Result<String, String>?

[diesieben07]

onErrorResumeNext expects an observable again, not a plain value

[diesieben07]

You probably want onErrorReturn instead

[diesieben07]

https://github.com/ReactiveX/RxJava/wiki/Error-Handling-Operators#onerrorreturn

[iex]

ah, too many things going on at once 🙂 thanks! It compiles now