from <https://kotlinlang.org/api/latest/jvm/stdlib...

# getting-started

[y]

from https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-array/get.html
"If the index is out of bounds of this array, throws an IndexOutOfBoundsException except in Kotlin/JS where the behavior is unspecified."

does this mean I can't rely on catching an IndexOutOfBoundsException here? (this is just curiosity, not trying to solve a specific issue)

[Sam]

That's how I'd interpret that line in the docs, for sure

[Sam]

If there's any doubt about whether the index is in range, I'd always go for getOrElse or getOrNull instead of get

[Sam]

I think it comes down to the fact that in JavaScript itself, indexing into an array just returns undefined if it's out of bounds

[Youssef Shoaib [MOD]]

Turns out that's because JS doesn't throw in an OOB case, it instead gives you undefined (because JS).

Edit: Sam beat me to the punch lol!

[y]

thanks for the answers. so JavaScript does JavaScript things, but why would calling this from Kotlin have unspecified behavior?

[y]

or does "Kotlin/JS" not mean what I think it means

[y]

(re: getOrNull - doesn't work in the case where you're indexing into a List<T?>, and so getOrNull returning null is ambiguous. which of course you can solve in other ways)

[Sam]

Well, having Kotlin/JS arrays behave the same as the JS arrays they're calling through to is probably the path of least resistance. "Unspecified" is kind of a cop-out; I would guess it basically means "it works one way right now, but we don't really like it so we might change it in the future"

[y]

a quick search told me that "Kotlin/JS" does indeed not mean what I think it means. now that I read about it, this all makes sense. well, TIL.

[Johann Pardanaud]

My personal approach to this was to check if the index is contained within the indices range:

if (index in myArray.indices) {
    println(myArray[index])
}

[Johann Pardanaud]

Before, I was trying to catch the errors, but it wasn't working for all targets

[y]

yeah, checking the index works.
and in the general case you could define some sort of tri-state sealed class and write a getOrNull equivalent that returns one of: class Exists(val T), object ExistsButNull, object OutOfRange.
or use some general Either<A, B> class and write a getOrNull equivalent that returns Either<T?, Unit> or something like that.
etc.