Suggestion: Add parFlatMapN

[TobiasRoland]

Motivation

I really like flatMap.

I also really like parMapN on tuples.

I therefore suspect I'd really love a parFlatMapN

currently:

val helloF: F[String] = (someF, someOtherF).parMapN((a,b) => "hello")
val worldFF: F[F[String]] = (someF, someOtherF).parMapN((a,b) => "world".pure[F])
val worldF: F[String] = stringFF.flatten

what I'd love to have:

val helloF: F[String] = (someF, someOtherF).parMapN((a,b) =>"hello")
val worldF: F[String] = (someF, someOtherF).parFlatMapN((a,b) => "world".pure[F])

Is there another way to accomplish this than parFlatMapN

Yep, but I think it'd be quite nifty to have it.
The argument against is I suspect that you can just do .parMapN(..).flatten - it's not that much more code to look at - but wouldn't the same argument apply to most flatMap operations (you could just do .map(...).flatten)?

It came up in a $DAYJOB example that looked not-really-but-kind-of-sort-of like this (using cats-effects IO here for the sake of the example)

def ioEnrichOrAbsent(thing: Thing): IO[Option[Enriched]] = ???

val enriched: IO[List[Enriched]] = (ioAPICall, ioSomeOtherAPICall).parMapN {
   (a,b) => {
      val listOfThings: List[Thing] = getListToTraverse(a,b)
      listOfThings
         .parTraverse(ioEnrichOrAbsent)
         .map(_.flatten)
   }
}.flatten

... which, yes, in this simplified could be refactored this to be more legible in a myriad ways. But, I still think parFlatMapN would have made it more obvious than a flatten (especially because I'm already using .flatten for the List[Option[A]]` inside the parMapN, so there's a bit of mental gymnastics people have to do to realize which thing is being flattened and why)

[danicheg]

It's a good suggestion! Generally speaking, there is a PR to cats with adding this method already. I've asked about its status, and feel free to vote about naming in that PR!

[TobiasRoland]

(if that PR goes through as flatParMapN, I'm opening a PR to mouse to add an alias that is parFlatMapN 😄 )

[TonioGela]

(if that PR goes through as flatParMapN, I'm opening a PR to mouse to add an alias that is parFlatMapN 😄 )

No worries, I'm the one who opened the PR on cats, and I just changed the function's name ;)

[TobiasRoland]

OK - I think that's me satisfied, I'll close this issue!