I know that kotlin accepts the following syntax ``...

# announcements

[Mikael Alfredsson]

I know that kotlin accepts the following syntax

fun <T> f(): Foo where T : Bar, T : Baz { ... }

but can I do the same with for example a map?
val map = mapOf<String, T (where T:bar, T:Baz)>

[Animesh Sahu]

Yes, this does work:

interface Interf
interface Interf2

class A : Interf, Interf2
class B : Interf, Interf2

fun main() {
    val list = listOf(
        A(),
        B()
    )

    test(list)
}

fun <T> test(list: List<T>) where T : Interf, T : Interf2 {

}

It has intersectional type

[Animesh Sahu]

Here's another reference if you like to check it out: https://stackoverflow.com/q/62241262/11377112

[Mikael Alfredsson]

So the check will be in the receiving function, not in the “listof”?

interface Interf
interface Interf2
interface Interf3

class A : Interf, Interf2
class B : Interf, Interf3
fun main() {
    val list = listOf(
        A(),
        B() // here I want this to fail.
    )
   list.forEach{
     val a = it as Interf
     val b = it as interf2 // this will be a runtime exception
   }
}

[Animesh Sahu]

You cannot intersectional specify the types actually, if you can define a use case I can better help?

[Animesh Sahu]

The functions can bound these to get correct types, but I don't see any need in this situation (local scopes)

[Mikael Alfredsson]

in my case above, i don’t really have a function and in my real life code, the list is a global list that is being used inside another function, but its not part of the functions parameters (since its a web server route function)

[Animesh Sahu]

And basically if you have all the types in your module (doesn't depend on other) you can always make a new interface combining both, and class which inherit it.

[Mikael Alfredsson]

I mean, i can live without it, but it would be nice to have compile time checks instead of runtime 🙂

[Mikael Alfredsson]

with listOf<Interf2>(A(), B()) the compiler would complain in my example, but I can only do that check for one interface.

[Animesh Sahu]

In my case above, i don’t really have a function and in my real life code, the list is a global list that is being used inside another function, but its not part of the functions parameters (since its a web server route function)

Best bet would be to define the list as List<Any> and provide the add/remove methods yourself and add constraints there.

[Animesh Sahu]

That's basically how arrays are handled in the backside inside the list tbh...

[Mikael Alfredsson]

Yes, I can probably find some nice workarounds, I was just curious if it was possible to do something like listOf<Interf & Interf2>(…)

[Animesh Sahu]

Currently, no. Check #language-proposals to discuss with devs.

[Mikael Alfredsson]

👍 Thanks for the input