It seems a bit odd that I'm required to explicitly state the return type of

Nothing

in this case...

fun justThrowIt(): Nothing = throw IOException()

...while here, I'm not:

fun justLoop() { while (true) {} }

The second function "returns" Unit.

I can explicitly state the return type as

Nothing

and it does still compile.

fun justThrowIt() { throw IOException() }

works too

No, it doesn't.

If you omit the return type, you've explicitly made it Unit.

my version is different from your version

If the method is an expression, then the return type is inferred.

@Andreas Sinz Oh gosh, you're right, it is different.

Oh is it?

Yeah:

val result = try {
    println("Doing some I/O...")
    true
} catch (e: IOException) {
    println("Oops!")
    false
} finally {
    println("""In the "finally" block...""")
}

That's try and catch, not throw.

Ahaha sorry.

Can you do,

val something = throw IOException()

?

Anyway, yeah:

val x = throw IOException()

Totally compiles.

Oh, had no idea. Weird.

And the type of

x

appears to be

Nothing

, at least it still compiles if I explicitly state it as such.

throw

always "returns"

Nothing

OK, cool.

and btw,

while

is a statement, so a while-loop doesn't return anything

Yeah that's true.

If

throw

"returns"

Nothing

, then why doesn't

fun justThrowIt() = throw IOException()

work? Strange.

So, as far as I can tell, in the case of

fun justLoop() { while (true) {} }

The return type is

Unit

. It does still compile if I explicitly state return type of

Nothing

. I'd guess that the compiler would enforce return type of

Nothing

if it were smart enough to know that the function never returns, but I guess it isn't.

@Dominaezzz it does work fine, you get the error Nothing return type needs to be specified explicitly so you don't accidentally return

Nothing

from a function

Oh okay. That makes sense.