Anybody can help me with this sentence

Question
1

the sentence is like this

  def run(args: List[String]): URIO[ZEnv, ExitCode] =
    init(args.headOption).use { case (executor, ctx) =>
      val appF = executor.run.compile.drain
      appF.run(ctx) as ExitCode.success
    }.orDie

this is from the ergodex amm excutor bot project.
I am new for scala, so it’s a little difficult for me to understand this entry point method, can anybody help me to explain this difinition block? or any hint is also welcomed.

thanks

2

Well, there are a lot of things going on there, starting from the fact that it is using an advanced library like ZIO which implies a different programming parading; one that folks of the typelevel community like to call “Programs as Values”.
It also seems to be interoperating with fs2 and probably cats-effect.

So yeah a lot of things going on which makes it hard to answer.
I would suggest moving your question to discord so we can tackle it bit by bit.
If you still prefer this space, that is okay but then it may help if you can be more specific about what you understand and what not; as well as your intention with such code.

4

thanks a lot.
I have understood this sentence. Yes it’s a zio app, and the “case” keyword leads a partical function as the single parameter of init().use function, and then the returned function value calls the orDie function. scala is really complex.

5

#init() returns a Resource which in turn has a #use() method that takes a (total) function as a parameter. In this case the argument is provided in partial function syntax, but the function actually is total - the syntax is only used to get destructuring pattern matching on the function parameter. (And yes, having PartialFunction extend Function1 probably is one of the more dubious design choices in the standard library.)

If you’re new to Scala, I’d suggest to first get comfortable with the core language and standard library before diving into a complex stack such as cats-effect/fs2/ZIO.

2 Likes
6

Agreed – it’s not so much that the Scala language per se is complex, it’s that you are combining several relatively complex libraries in one little bit of code there. That’s an enormous amount to bite off at once: I usually spend several months (and several books) getting new engineers up to speed on the languages plus all of those components.

1 Like
7

thanks, in fact I am learning a sdk and this is an example. so a little difficult for me to understand this sentence. but now I know how it works, thanks again.