Move contain_ to UnorderedFoldable

[BalmungSan]

No description provided.

[armanbilge]

Note that this will be source-breaking for anyone relying on something like import cats.syntax.foldable._ instead of a catch-all. I think this is probably ok?

[satorg]

I'd suppose, it might be reasonable to add contains_ to the UnorderedFoldable type class itself. Because potentially it could be overridden with more efficient implementations when applicable.

[armanbilge]

Good point, that may very well be the case when #4147 materializes :)

[BalmungSan]

@satorg @armanbilge I move it to UnorderedFoldable as contains and the constains_ extension now forwards to the instance method.

I assume I should test it, but not sure what would be a good test?
All I can think of is ensuring it is consistent with the exists version.

[satorg]

I'd suggest two ways to test it: as you said, consistency with exists, and also consistency with Set#contains might be useful as well. I assume, Set implements UnorderedFoldable – is that correct?

[BalmungSan]

@satorg I just pushed the tests, let me know what you think.

[satorg]

Note that this will be source-breaking for anyone relying on something like import cats.syntax.foldable._ instead of a catch-all. I think this is probably ok?

Well, seems that import cats.syntax.foldable._ makes available the syntax for UnorderedFoldable as well:

trait FoldableSyntax extends Foldable.ToFoldableOps with UnorderedFoldable.ToUnorderedFoldableOps {
   ???
}

So we should be safe there (not sure if it makes sense to write a test for that though)...

[satorg]

You may need to add the new laws created to the cats.laws.discipline.UnorderedFoldableTests. Otherwise these new laws will have no effect on real laws-checking tests.

[BalmungSan]

You may need to add the new laws created to the cats.laws.discipline.UnorderedFoldableTests. Otherwise these new laws will have no effect on real laws-checking tests.

Oh, right, that explains why the original buggy law did not fail the tests.
Sorry about that, I was not familiar with how the laws are organized.

But I just pushed that change plus the two extra laws you proposed!

[armanbilge]

This looks great! Just some tiny nits :)

[armanbilge]

🎉