Hello, It looks like Kotlin 1.4 is bringing new st...

# announcements

[Elka]

Hello,
It looks like Kotlin 1.4 is bringing new stuff! Any reason why this breaking change?
Code

fun <T: Any> x(block: () -> T?) {
    val res = block()
    if (res != null) {
        println(res)
    } else {
        println("returned null")
    }
}

fun test() {
    x<Unit> {
        null
    }
}

Kotlin (<1.4)
It prints "retuned null
Kotlin (>= 1.4)
It prints kotlin.Unit

The weird part is that x { null } works fine. The compiler is able to infer the type to Unit?. But I can't write x<Unit?> { null } as the type is bound to Any which is something we need on Kotlin-Native (unless this has changed too)

[Tobias Berger]

I can't tell you why 1.4. lets the lambda return Unit instead of the last statement which is null, but what you call "the weird part" isn't really weird at all. The type Unti? isn't inferred, it's specified. The return type of `x`'s lambda parameter is T?, so because your call explicitly specifies T as Unit, the lambda return type is Unit?

[ilya.gorbunov]

This looks much like https://youtrack.jetbrains.com/issue/KT-41005 and this issue is fixed in 1.4.10. Could you upgrade to that new version and check whether it happens then?

[Elka]

@ilya.gorbunov Thanks for your help. This has been fixed in 1.4.10