sorry that this is convoluted, but it's pretty clo...

# getting-started

[y]

sorry that this is convoluted, but it's pretty close to the real code:

sealed class Base() {
    abstract val bar: Bar
    
    fun interface Bar {
        fun frobnicate(a: Int, b: String)
    }
}

class Derived : Base() {
    override val bar: Bar get() = ::DC // ERROR: Return type mismatch: expected 'Base.Bar', actual 'Function2<Int, String, Unit>'.
}

data class DC(val a: Int, val b: String)

vs

sealed class Base(val bar: Bar) {
    fun interface Bar {
        fun frobnicate(a: Int, b: String)
    }
}

class Derived : Base(::DC) // works

data class DC(val a: Int, val b: String)

the second one compiles. how do I get the first one to compile? do I require an explicit cast to Bar?

EDIT: is it because `fun interface`s get "promoted" when passed directly like this?

[Youssef Shoaib [MOD]]

I think it has to do with Unit conversion? the constructor doesn't return Unit, but I guess function calls allow for unit conversion, while standalone values don't?
Edit: nvm, even using a Unit-returning function here doesn't make it compile

[Youssef Shoaib [MOD]]

FYI you can use the conversion function that gets created for every fun interface:

sealed class Base() {
    abstract val bar: Bar
    
    fun interface Bar {
        fun frobnicate(a: Int, b: String)
    }
}

class Derived : Base() {
    override val bar get() = Bar(::DC)
}

data class DC(val a: Int, val b: String)

[y]

hey that works! would never have figured that out.

[y]

another thing that worked is removing the fun interface, making frobnicate an abstract fun and writing override fun bar(a: Int, b: String) = DC(a, b)
(however override fun bar(a: Int, b: String) = ::DC did not)