Similar question to the above, but with covariance...

# announcements

[Matej Drobnič]

Similar question to the above, but with covariance this time.

If I undestand correctly:

* T is String
* out T means that String or any of its subtypes can fit this
* Since String in methodB matches that, why I can't pass methodB into methodA?

Untitled

[Petter Måhlén]

i think you’re declaring the variance in the wrong place. you’re saying methodA needs a container out String as its parameter, and you’re passing in a container String , which isn’t the same. if the container data class was defined as out T , and methods A and B just specified as T, I think it would be different. in both the cases. i don’t have the time right now to work it all out, but that would be my guess 🙂

[Tomasz Krakowiak]

Because, by type signature of methodB, it may perform invariant operation on input. Let's say Container would have method set(value : T) - functionB is allowed to call it, but it's not allowed to call it on Container<out *>

[Tomasz Krakowiak]

To be more illustrative:

data class Container<T>(var value: T)

fun methodB(input: Container<String>) {
	input.value = "B"
}

[Matej Drobnič]

aaaah I see

[Matej Drobnič]

thanks a lot!