Hey guys! While reviewing PR I've spotted a smell...

# announcements

[Kamil K]

Hey guys!

While reviewing PR I've spotted a smelly code.

fun x(anInt: Int) : String {
    when (anInt) {
        0 -> return "zero"
        1 -> return "one"
    }
    return null!!
}

Despite the 'quality` of code itself I'm curious why compiler thinks that return null!! is fine (IDE hints that return statement is unreachable which is false)?
And similarly why this val a : Int = null!! is allowed as well.

[gian]

Because it is as fine as throw Exception()

[gian]

the return is unreachable, as the exception will be thrown before returning

[marstran]

null!! has type Nothing, which is a subclass of every type. You can therefore return it from everything (for the same reason you can throw exceptions). The return is unreachable because there is an expression of type Nothing before it.

[Kamil K]

Cool beans, checked with decompiled code and make sense.

[karelpeeters]

The type of null is `Nothing?`:

[marstran]

Yes, therefore the type of null!! becomes Nothing.

[Paul Woitaschek]

I'd move the return out of the when block and use an else -> error("Invalid anInt=$anInt")