~Is the only reason to use `: Any` in generics to ...

# getting-started

[dave08]

Is the only reason to use : Any in generics to prevent nulls? I have something like:

interface UseCase<in Request : Any, out Response : Any> {
    suspend fun execute(request: Request): Response
}

and in certain cases I need the Response to be nullable, and in others not. How can I implement such a Spy:

class UseCaseSpy<Request : Any, Response>(
    private val returnIfNoResponse: (suspend (Request) -> Response)? = null,
    private val allowNullResponse: Boolean = false
): UseCase<Request, Response> {
    var request: Request? = null
    var responseToReturn: Response? = null

    override suspend fun execute(request: Request): Response {
        this.request = request

        val response =  responseToReturn ?: returnIfNoResponse?.invoke(request)

        if (response == null && !allowNullResponse)
            error("Either responseToReturn or returnIfNoResponse needs to be provided.")

        return response
    }
}

execute needs to return Response? whether my actual type is nullable or not... so it just doesn't compile

[Youssef Shoaib [MOD]]

You need to define the interface like this:

interface UseCase<in Request : Any, out Response : Any> {
    suspend fun execute(request: Request): Response?
}

Then it should all work fine hopefully

[dave08]

Nope, response still with red squiggly...

[dave08]

It wants the Response being returned from exectute to be Response?

[dave08]

I guess this is the problem: https://medium.com/@igorwojda/kotlin-deep-dive-into-generics-nullability-9853d9a9f50d

[dave08]

Doesn't seem possible for the compiler to infer such things...

[dave08]

But like you said, removing the : Any from the interface works... just for the UseCaseSpy I'm forced to return Response? ...