```interface IS lt T gt fun lt T gt T fmap T sealed class IIS lt T gt IS lt T gt data class IntIS lt Int gt val x Int IIS lt Int gt fun Int fmap return x+1 ```

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
    }
}

how to fix this?

deactivateduser

06/28/2020, 2:31 PM

what were you trying to achieve?

Ifvwm

06/28/2020, 2:35 PM

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

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

generics constraints + interface + class extension

ad-hoc polymorphism

deactivateduser

06/28/2020, 2:43 PM

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

Kroppeb

06/28/2020, 2:47 PM

https://pl.kotl.in/eeCtCLyZz

Ifvwm

06/28/2020, 3:03 PM

why

return this

can't be

return x+1

in your code? there's (val x: Int) in the constractor

deactivateduser

06/28/2020, 3:25 PM

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

06/28/2020, 3:28 PM

why? x declared as Int, and the function return Int, so why

return x+1

won't be Int?

Kroppeb

06/28/2020, 4:57 PM

What are you talking about?

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

https://pl.kotl.in/riHjjdVkj

The issue was that you were shadowing the

Int

type