Smartcasting a function type property seems to not work.

class Foo(val callback: (() -> Unit)? = null) {
    init {
        if (callback != null) {
            callback() // Error: Reference has a nullable type '(() -> Unit)?'
        }
    }
}

This works fine:

class Foo(callback: (() -> Unit)? = null) {
    init {
        if (callback != null) {
            callback() // Error: Reference has a nullable type '(() -> Unit)?'
        }
    }
}

And this too:

class Foo(val callback: (() -> Unit)? = null) {
    init {
        if (callback != null) {
            callback.invoke()
        }
    }
}

Yup, looks like a bug to me as well. - it's in an init block, no race conditions are possible - it's a immutable

val

, cannot be changed after being set Smart cast should be able to figure that out, and it does in the 3rd example.

how will it if check by 'is'?

https://youtrack.jetbrains.com/issue/KT-4113 No smartcast for nullable lambda property (functional type) with implicit/operator

invoke

call

6 years ago? Wow, this seems like it would be easy to fix though.