Handle Kotlin Result<T> types on Swift side, similarly as we have it in Kotlin

[developer--]

In cases where most of the shared logic is already written using Kotlin Result types, instead of changing return type everywhere it would be great if iOS devs will be able to handle it like this:

someResult.onSuccess { obj ->
   ...
}.onFailure { ex ->
   ...
}

[burnoo]

The reason behind it is that Result is a value/inline class and those are not supported by Swift/Objective-C interop (source). Generic inline classes are unfortunately compiled as Any?, so extensions are not available as the type is erased.

To allow using inline classes in Swift another feature could be added to SKIE - converting inline classes back to regular classes for iOS target (or data classes for equals/hashCode compatibility). The performance boost of using inlining will be lost, but the type safety will be achieved in exchange. That could be probably done in Frontend IR phase of the compilation.

Another issue would be that Result extensions are functions on a generic class, so the compiled typed lambda argument will be visible in Swift as Any? (onSuccess(action: @escaping (value: Any?) -> Void)). To resolve this problem extensions could be reimplemented in Swift.