Collect all of the successes and failures of a sequence of ZIOs together?

user_446554 0
Viewed 203

I have a bunch of IOs, all of which may have either succeeded or failed:

val result: Seq[IO[MyFailure, MySuccess]] = ...

I need to summarize the results such that I can examine all the failures and all the successes together:

case class MySummary(failures: Seq[MyFailure], successes: Seq[MySuccess])
def makeSummary(results: Seq[IO[MyFailure, MySuccess]]): UIO[MySummary] = ???

At first this seemed quite similar to foreach, but upon closer inspection I see that that doesn't help here. For Future I'd normally use sequence, and for Seq[Either[A,B]] I could use partitionMap. What is the equivalent method in ZIO named?

zio scala
2 Answers

I'm not familiar with ZIO, there might be a built-in way to achieve the same.

I would go with something like the following:

def makeSummary(results: Seq[IO[MyFailure, MySuccess]]): UIO[MySummary] = {
  results.foldLeft(ZIO.succeed(MySummary(Seq(), Seq()))) { (acc, io) =>
    acc.flatMap { summary => 
      io.fold(
        err => summary.copy(failures = summary.failures :+ err),
        suc => summary.copy(successes = summary.succcesses :+ suc)
      )
    }
  }
}
user_53891270

You can't examine all failures with Future.sequence, you will only get back the first failure if there is any.

The ZIO equivalent for Future.sequence would be ZIO.collectAll which is pretty much equivalent to ZIO.foreach(result)(identity).

If you really need to accumulate all errors then you should probably use ZIO.validate and for partitioning there's also ZIO.partition.

Some code for comparison:

  val result: Seq[IO[MyFailure, MySuccess]] = ???

  val withCollectAll: IO[MyFailure, Seq[MySuccess]] = ZIO.collectAll(result)
  val withForeach: IO[MyFailure, Seq[MySuccess]] = ZIO.foreach(result)(identity)
  val withValidate: IO[::[MyFailure], Seq[MySuccess]] = ZIO.validate(result)(identity) //`::` just means that the list cannot be empty
  val withPartition: UIO[(Iterable[MyFailure], Iterable[MySuccess])] = ZIO.partition(result)(identity)

Code for makeSummary with ZIO.partition:

  def makeSummary(results: Seq[IO[MyFailure, MySuccess]]): UIO[MySummary] =
    ZIO.partition(results)(identity).map { case (f, s) => MySummary(f.toSeq, s.toSeq) }
user_120664680
Related