Hi people, Does kotlin support exhaustive when wit...

# android

[Sergio C.]

Hi people,
Does kotlin support exhaustive when without assigning a variable or without libraries?

[ephemient]

https://youtrack.jetbrains.com/issue/KT-12380

[ephemient]

https://github.com/cashapp/exhaustive has a list of options

[Vampire]

If you decide to go the assignment way, you could at least make it look fancy by making it a face watching the exhaustiveness like `val _ =` or val o_O =. :-)

Another way that is not an assignment, does not need a library, does not pollute the Any namespace and does not impact runtime performance as it is an inlined no-op is this variant:

when (...) {
    ...
}.let { /* it be exhaustive */ }

[Javier]

There were another approach via object + infix function so you get:

Do exhaustive when (...) { }

[Vampire]

Hm, also nice, though with runtime effect as it cannot be inlined to a no-op, right?

[Javier]

I think so

[ephemient]

Proguard/R8 could be configured to eliminate it

[ephemient]

but even so, I would expect a hack like

val Do: Nothing?
    inline get() = null
infix inline fun Any?.exhaustive(`when`: Any?) = Unit

to have no runtime impact

[Sergio C.]

That's nice options I need to try.

[Sergio C.]

How would you use that @ephemient?

[ephemient]

https://kotlinlang.slack.com/archives/C0B8M7BUY/p1622672807405500?thread_ts=1622670909.404500&cid=C0B8M7BUY

[ephemient]

personally I would just throw a .let {} on the end, though

[Vampire]

the infix fun on Any?

[Vampire]

Shouldn't it be more like

object Do {
    inline infix fun exhaustive(`when`: Any?) = Unit
}

[Vampire]

Or do you expect runtime impact on that version?

[Javier]

Yeah, with the object you are not forced to use Any to avoid suggesting it for everything

[Sergio C.]

Kotlin needs to release an official Exhaustive when...

[Javier]

I think it will be in 1.6

[ephemient]

@Vampire with the object version, you still have the runtime impact of Do.getInstance()

[Sergio C.]

Cool, we are near.