Hello! I'm updating from Arrow 1.1.3 to 1.1.5, and migrating the deprecations in the Either API. Whi...

# arrow

[Marc Plano-Lesay]

Hello! I'm updating from Arrow 1.1.3 to 1.1.5, and migrating the deprecations in the Either API. While most of them make sense and have very clear/simple replacements, I find filterOrElse to be a bit annoying - while implementing something similar with flatMap is easy enough, it loses quite a lot in terms of readability. 🧵

[Marc Plano-Lesay]

Here's what I used to have:

.filterOrElse {
        predicate = { userAccountManager.hasSession(it) },
        default = { SignInError.Internal },
      }

And with `flatMap`:

.flatMap {
        if (userAccountManager.hasSession(it)) {
          Right(it)
        } else {
          Left(SignInError.Internal)
        }
      }

[Marc Plano-Lesay]

Previously, the intention was obvious just by reading the filterOrElse name - which is not the case at all anymore. Is there a more expressive way to replace filterOrElse that I'm missing?

[Stylianos Gakis]

Filter makes me think of lists tbh. filterOrElse doesn’t sound intuitive at all not gonna lie 😄
As someone who hadn’t seen this function before, I’d much prefer to see

.flatMap {
  if (userAccountManager.hasSession(it)) {
    it.right()
  } else {
    SignInError.Internal.left()
  }
}

In fact, I’d personally rather see something like this instead

val x = either<SignInError, Session?> {
  val session: Session = Session // you had this before the flatMap, might need to `bind()` here
  ensure(userAccountManager.hasSession(session)) { SignInError.Internal }
  session
}

[Marc Plano-Lesay]

I guess this either block + ensure might be the better option indeed. Thanks, I hadn't considered that one!

[Stylianos Gakis]

Yeah do give it a try and tell us how it went for you. I personally find myself opting for that style more often than not lately.

[Marc Plano-Lesay]

I quite like the flowable style of chaining calls, but it does indeed require knowing the API inside and out where a more imperative style is usually clear to anyone