Iterable test

[abendt]

this adds a couple of tests to IterableTest to improve test coverage for functions in Iterable

#2894

[abendt]

i think there is a bug in the implentation of unalign. How i understand it align should be the inverse of unalign: align(unalign xs) shouldBe xs.

However this only works if all xs have both values. Then the current implementation of unalign will split the input into two list of equal length:

val xs = listOf(Both(1,x), Both(2,y), Both(3,z))
val (l,r) = xs.unalign() // listOf(1,2,3) to listOf(x,y,z)
l.align(r) shouldBe xs 

with this its possible to align both lists and to get back to the initial value of xs.

If xs contains Left or Right values then the splitted lists will have differing length. This leads to elements end up in a wrong position in the list:

val xs = listOf(Left(1), Both(2,y), Right(z))
val (l,r) = xs.unalign() // listOf(1,2) to listOf(y,z)
l.align(r) shouldBe xs // wrong! actual value is listOf(Both(1,y), Both(2,z))

One way to fix that could be to let unalign return Pair<List<A?>, List<B?>>. Missing elements in the source would then be represented as null in the result

[nomisRev]

Hmm, interesting find @abendt. Thank you, great work!

This would be breaking, and would thus need to land in 2.0.0. In a PR I am preparing for some deprecations for Iterable.kt I actually wanted to rename unalign to seperateIor because it's behavior matches seperateEither and not unalign as you mention here.

Not sure what is the best path forward though 🤔 I think it would be best to create a separate PR against the arrow-2 branch changing the unalign signature, and adding these tests there. Then we can update this PR with the seperateIor introduction, and relevant tests. Feel free to take this change from my WIP into to your PR:

public fun <A, B> Iterable<Ior<A, B>>.seperateIor(): Pair<List<A>, List<B>> =
  fold(emptyList<A>() to emptyList()) { (l, r), x ->
    x.fold(
      { l + it to r },
      { l to r + it },
      { a, b -> l + a to r + b }
    )
  }

@Deprecated(
  "The current unalign function is renamed to seperateIor, and a new unalign function is going to be added to Arrow 2.0.0.",
  ReplaceWith("seperateIor()", "arrow.core.seperateIor")
)
public fun <A, B> Iterable<Ior<A, B>>.unalign(): Pair<List<A>, List<B>> = seperateIor()

WDYT? Are you interested in adding such a PR against arrow-2? And making the other relevant changes here?

[abendt]

yes, i will make the changes here and create a new PR

[nomisRev]

Awesome, thank you so much @abendt 🙏 👏 👏

[abendt]

i have reverted the generator implementation so the tests are passing again.
also added the deprecations as discussed (also added a deprecation for the 2nd unalign function, as we have the same problem there)

[abendt]

hey @nomisRev, some of the gitlab checks fail because of timeouts. think this is not related to my changes? any idea how to resolve them?

[nomisRev]

It's unrelated to your changes @abendt, it's been a long standing issue on Gradle side and the fix has finally been merged and released in 7.6. I created a PR to bump the timeout on CI. #2965

[nomisRev]

Awesome work @abendt! 🙌 🥳 Thank you 🙏