Hi Anyone tried to typealias an `expect`ed class? ...

# multiplatform

[albertosh]

Hi
Anyone tried to typealias an `expect`ed class? Looks like I can do it for the JVM but not for JS. The aim is to provide a “platform native” output for some functions so they can be used from Java/Js

My common code

expect class Wrapper<T: Any?>

Working Kotlin for JVM code

actual typealias Wrapper<T> = CompletableFuture<T>

Not working Kotlin for JS code

actual typealias Wrapper<T> = Promise<T>

Compiler claims that
Aliased class should not have type parameters with declaration-site variance

Any clue?

[Big Chungus]

+

[russhwolf]

typealias needs to be an exact signature match. Promise is declared as open class Promise<out T> and the out and open are missing in your expect statement.

[albertosh]

I see
In the end, I ended up wiring things manually. Not as nice & clean as just typealiasing stuff but works as well
Common code

internal expect fun asyncWrapper(body: suspend () -> ExperimentJournal?): AsyncWrapper<ExperimentJournal?>

expect class AsyncWrapper<T: Any?>

JVM code

internal actual fun asyncWrapper(body: suspend () -> MyClass?): AsyncWrapper<MyClass?> =
        GlobalScope.future {
            body()
        }

actual typealias AsyncWrapper<T> = CompletableFuture<T>

JS code

internal actual fun asyncWrapper(body: suspend () -> MyClass?): AsyncWrapper<MyClass?> {
    return AsyncWrapper(GlobalScope.promise {
        body()
    })
}

actual class AsyncWrapper<T : Any?>(
        internal val promise: Promise<T>
) {
    @JsName("then")
    fun <S> then(onFulfilled: ((T) -> S)?, onRejected: ((Throwable) -> S)?): Promise<S> = promise.then(onFulfilled, onRejected)

    @JsName("catch")
    fun <S> catch(onRejected: (Throwable) -> S): Promise<S> = promise.catch(onRejected)
}

suspend fun AsyncWrapper<Any>.await() = promise.await()

I don’t actually like much the JS one. I tried to extend Promise but I kept getting some undefined related errors, so I had to replicate some code. In the end, it’s not that much code to replicate

[albertosh]

Main idea is that in JVM it will be handled as CompletableFuture and in JS as Promise
It’s just an “output” type of the library, so it will not be used internally