Make useForever polymorphic rather than speciailising it to Nothing

[george-wilson-rea]

I'd prefer if I could pick a type for this, eg. ExitCode.

I write apps like this:

class MyApp extends IOApp {
  def run(args: Args): IO[ExitCode] =
    for {
      config <- readConfig
      otherStuff <- setUpOtherStuff(config)
      ec <- httpServer.resource.useForever
    } yield ec
}

and with the Nothing type, the Scala compiler warns me about dead code, but if I use httpServer.resource.use(_ => IO.never[ExitCode]) then it works fine. Hence, I propose changing useForever to work like this.

[durban]

I might be missing something obvious, but I tried your example code, and this change did not make the warning disappear: the compiler still inferred ec: Nothing . (On the other hand, using https://github.com/oleg-py/better-monadic-for does make the warning go away, probably because it removes the final map call.)

[djspiewak]

I concur with @durban: I'm not sure this really helps. The type will still be inferred to Nothing in unascribed cases, which in turn recreates the problem. There are also a number of cases that I can't quite remember (I think only on Scala 2.12?) where the Nothing encoding actually works a lot better than [A] A, even though they should be equivalent.