Holy moly. What witchcraft is this? IntelliJ will,...

# intellij

[robin]

Holy moly. What witchcraft is this? IntelliJ will, on an await call, actually statically check the job that you're awaiting, and give you an "Unreachable Code" warning if that job will always fail? That's either some very specific inspection or some seriously impressive general static analysis

[dsavvinov]

I haven’t checked, but I’m pretty sure that it’s actually neither of these — it’s the smart type system and inference 🙂

I guess that async returns something like Deferred<T>, and Deferred<T>.await returns T.

Then, throw Exception() actually has type in Kotlin — it’s Nothing. So, type of job2 is Deferred<Nothing> and job2.await() returns Nothing.

Now, the compiler is smart and knows that you can’t get a value of type Nothing, so if something appears to return Nothing, it actually means that the execution flow is interrupted (e.g. by exception)

[robin]

Ohhh, of course, that's it 🤦 I continue being amazed by kotlin's type system 😄

[robin]

Thanks for pointing that out!

[dsavvinov]

No problem, that’s actually non-trivial interaction 🙂

[Paul Woitaschek]

It's actually pretty trivial

[Paul Woitaschek]

Rule 1: sth that just throws returns a nothing

[Paul Woitaschek]

Rule 2: everything after nothing is unreachable

[Paul Woitaschek]

Almost all inspections are trivial, that's why they are so genious when they play together like this :)

[dsavvinov]

Yeah, that’s actually what I wanted to say, but failed to 😅 All pieces individually are not that complicated, but they play nicely together and sometimes cover quite non-trivial cases 🙂