```interface IS<T> {fun <T>T.fmap():T}...

# announcements

[Ifvwm]

interface IS<T> {fun <T>T.fmap():T}
sealed class IIS<T>: IS<T>
data class IntIS<Int>(val x:Int): IIS<Int>(){
    fun Int.fmap(){
        return x+1
    }
}

[Ifvwm]

how to fix this?

[deactivateduser]

what were you trying to achieve?

[Ifvwm]

if a parameter declare has IIS<T>, so I can put a value has IntIS<Int> on there, and this value has fmap method, just like a typeclass

[Ifvwm]

create a typeclass IS, and require to implement function fmap, then make Int and String as IS's instances, then where a parameter declare it has IS, then I can put Int or String value on there, and that value must have fmap function

[Ifvwm]

generics constraints + interface + class extension

[Ifvwm]

ad-hoc polymorphism

[deactivateduser]

something like this? https://pl.kotl.in/u3IuTUInI... not really sure what is your use case... it looks overly complicated design...

[Kroppeb]

https://pl.kotl.in/eeCtCLyZz

[Ifvwm]

why return this can't be return x+1 in your code? there's (val x: Int) in the constractor

[deactivateduser]

u can replace the this with x+1 and the compiler will tell you why that one cannot be done... 😉.. basically, the returned type is different...

[Ifvwm]

why? x declared as Int, and the function return Int, so why return x+1 won't be Int?

[Kroppeb]

What are you talking about?

[Kroppeb]

I noticed a mistake from copying Handra's playground, as I was (and still am) on phone.

[Kroppeb]

https://pl.kotl.in/riHjjdVkj

[Kroppeb]

The issue was that you were shadowing the Int type