Hey guys I m trying to consume a sealed class on the iOS sid

Question

Hey guys I m trying to consume a sealed class on the iOS side In iOS the method return a completion handler with `SessionManagerCheckInResult lt UserInfo gt ` being `SessionManagerCheckInResult` is the sealed class ``` sealed class CheckInResult lt out T Any gt data class Success val data UserInfo CheckInResult lt UserInfo gt data class Error val exception Throwable CheckInResult lt Nothing gt ``` I m trying to get the error when I receive one but I m not able to get the result or error separated here What I get if I print the object is ``` Optional lt SharedSessionManagerCheckInResult gt some Error exception=ApiError code=400112 message=Invalid or missing members in payload ``` How can I get this error in iOS side Some way I can convert the data to a `SharedSessionManagerCheckInResultError` here

Sam · Answer

Check your bridging header for the full name of your class It ll be something like `SessionManagerCheckInResultError` then just try to cast it ```if let err = result as SessionManagerCheckInResultError Do error handling Or guard let userInfo = result as SessionManagerCheckInResultSuccess lt UserInfo gt Error handling here ```

Charles Prado · Answer

it seems that there s something wrong with these headers

Charles Prado · Answer

what I have here is ``` RESULT attribute swift name SessionManagerCheckInResult interface SharedSessionManagerCheckInResult lt covariant T gt SharedBase instancetype init attribute swift name init attribute objc designated initializer + instancetype new attribute availability swift unavailable message= use object initializers instead end ERROR attribute objc subclassing restricted attribute swift name SessionManagerCheckInResultError interface SharedSessionManagerCheckInResultError SharedSessionManagerCheckInResult lt SharedKotlinNothing gt instancetype initWithException SharedKotlinThrowable exception attribute swift name init exception attribute objc designated initializer instancetype init attribute swift name init attribute objc designated initializer attribute unavailable + instancetype new attribute unavailable SharedKotlinThrowable component1 attribute swift name component1 SharedSessionManagerCheckInResultError doCopyException SharedKotlinThrowable exception attribute swift name doCopy exception BOOL isEqual id Nullable other attribute swift name isEqual NSUInteger hash attribute swift name hash NSString description attribute swift name description property readonly SharedKotlinThrowable exception attribute swift name exception end ```

Sam · Answer

I have something similar in my project but I never try to switch over the type ```sealed class RailResult lt out V out E gt Represents a successful RailResult containing a value data class Success lt out V gt val value V RailResult lt V Nothing gt Represents a failed RailResult containing an error data class Failure lt out E gt val error E RailResult lt Nothing E gt fun valueOrNull V = when this is Success gt this value else gt null val isSuccess Boolean get = when this is Success gt true else gt false fun failureOrNull E = when this is Failure gt this error else gt null val isFailure Boolean get = when this is Failure gt true else gt false ```

Sam · Answer

Instead I just use the `valueOrNull` and `failureOrNull` methods with `guard` and `if let` statements

Charles Prado · Answer

Thanks < Sam> I think this can help me improving legibility here However I still wasn t able to figure out why I m not able to cast my data to `SessionManagerCheckInResultSuccess` or `SessionManagerCheckInResultError` do you see anything that could be wrong in my sealed class

Sam · Answer

I wrote this code about 2 years ago and probably ran into the same issue that you did I tried using a switch on my result class and get the same compiler warnings It s likely a limitation in the ObjC lt gt Swift bridging ObjC generics are very limited

Sam · Answer

Here s a trick you can do that will make the code a little more idiomatic Swift Usually you see `switch` statements done over enums with associated values rather than trying to cast it into something Here s an enum that wraps the result object I m using ```enum RailResultEnum lt T AnyObject E KotlinError gt case Success result T case Failure error Error static func fromResult rail RailResult lt T E gt gt RailResultEnum if let r = rail valueOrNull rail isSuccess return Success result r else return Failure error rail nserrorOrNull NSError domain Kotlin code 1 userInfo NSLocalizedDescriptionKey Uknown error in converting to Cocoa Error ``` You can then switch over it like this ```switch RailResultEnum fromResult rail result case Success let value print success value case Failure let error print failed error ``` It has some limitations A null in a nullable result will fall through to the error condition T can t be a primitive it has to be a class type

Charles Prado · Answer

Hi < Sam> Today I tested your suggestion and it worked for me tada tada tada I m still only using the base solution just replaced my `CheckInResult` with your `RailResult` class Now I m able to intercept the error ``` static func signIn idToken String serverAuthCode String gt Future lt UserInfo Error gt return Future promise in signIn idToken idToken serverAuthCode serverAuthCode data in if let userInfo = data valueOrNull promise Result success userInfo else if let = data failureOrNull TODO map the error promise Result failure AppError unknown ``` Thanks so much for this I m still a little bit curious why the other solution didn t work Not so sure I had seen some similar implementations in some other GitHub repos My bg is in iOS programming so there s some stuff that still doesn t make so much sense to me hehe

Sam · Answer

Same here my bg is more iOS focused I m glad the solution worked for you