Hey guys, i have a question, how do we handle Either response in iOS for KMM Like if it's Either<...

# multiplatform

[Srijit Saha]

Hey guys, i have a question, how do we handle Either response in iOS for KMM
Like if it's Either< Type_A , Type_B >
How do i get the values of Type_A and Type_B ?

[Sam]

I ended up writing an enum in swift to represent the Either type and a util to convert from the Kotlin one to the Swift one

It wasn't particularly pretty but works 🤷

[Andrei Salavei]

The Swift has *enum* Result<Success, Failure> *where* Failure : Error type that can be helpful, you can adopt it, or elaborate your situation a bit to find other solutions.

[Srijit Saha]

Can you give me a sample of how that util class looks like ?

[Srijit Saha]

I tried the result one, but i am not able to access it

[Srijit Saha]

Sorry, i am a complete noob in iOS

[Andrei Salavei]

Could you please describe you situation a bit more clear? Are you want to pass Either type from KMM library to swift and convert it there to some native type?

[Srijit Saha]

ok so in my KMM module I have a Either class where it can either be a data class if it's success and String class if it's a failure, which i am exposing, in android i can do it easily but in iOS i am having problems on accessing the inner data classes

[Andrei Salavei]

Okay, i see. If you could not access some class from swift, it means it wasn’t propagated into framework header file. It could be done it 2 ways: tell compile to import all classes from particular module or do simple hack (pit it somewhere inside iosMain module on Kotlin side)

fun Either.Value<*>.foo() {}
fun Either.Error<*>.foo() {}
fun Either<*>.foo() {}

After that it just a technical question how you want to handle it is Swift:

func handle<ValueType>(result: Either<ValueType>) {
    switch either {
    case let value as EitherValue<ValueType>:
        print(value.value!)
    case let error as EitherError<ValueType>:
        print(error.message)
    default:
        fatalError("Unexpected type")
    }
}

Note that Either type can be named a bit differently after KMM interop. In our case it called Platform_apiEither<T> and Platform_apiEitherValue<ValueType> and Platform_apiEitherError<ValueType>

[Werner Altewischer]

I assume you have a sealed class?

sealed class Either<T: Any> {
    class EitherValue<T: Any>(val value: T): Either<T>()
    class EitherError<T: Any>(val error: Throwable): Either<T>()
}

In Swift you can handle that as follows:

let either: Either<ValueType> = ...

if let eitherValue = either as? EitherValue<ValueType> {
   // code for value
} else if let eitherError = either as? EitherError<ValueType> {
   // code for error
}

[Srijit Saha]

sealed class Either<out S, out T> {

    data class Fail<out S> internal constructor(val failureCause: S) : Either<S, Nothing>() {
        companion object {
            operator fun <S> invoke(f: S): Either<S, Nothing> = Fail(f)
        }
    }

    data class Success<out T> internal constructor(val successResponse: T) : Either<Nothing, T>() {
        companion object {
            operator fun <T> invoke(s: T): Either<Nothing, T> = Success(s)
        }
    }
}

[Srijit Saha]

I have it like this

[Srijit Saha]

@Andrei Salavei ok, i will try it out