How to handle error or return value with a method

Question

I want to test, if the value is a Throwable, if it is, I want to print out an error message.

If the value is not a Throwable, I want to return it.

I have this code, which gives me following error message, when Im hovering over the "value" which sould be returned in the last line:

Found: (value : Either[Throwable, A]) Required: A )

def throwAndPlayAgainOrGet[A](value: Either[Throwable, A]): A =
{
    if(value.isLeft) println("error: " + value) + playAgain
    value
}

My Question:

how can I do that?

also asked at users.scala-lang.org/t/how-to-handle-error-or-return-value/8609 — Seth Tisue
– Seth Tisue, Commented Jun 27, 2022 at 16:30
Okey, so you found a throwable, you print it, and now what? Does the program stop? — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Jun 27, 2022 at 16:32
@LuisMiguelMejíaSuárez no the program is calling the playAgain function with the following signature: def playAgain: ZIO[Console, Throwable, Has[Any]] — helloworld
– helloworld, Commented Jun 28, 2022 at 6:07
I don't understand exactly how to fits the code you provided, but anyways. It seems you should rather lift that Either into the ZIO — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Jun 28, 2022 at 12:57

Guru Stron · Accepted Answer · 2022-06-27 08:01:41Z

2

You can use pattern matching for this:

def throwAndPlayAgainOrGet[A](value: Either[Throwable, A]): A = value match {
  case Left(err) => {
    println(err)
    someDefaultAValue // or throw err
  }
  case Right(v) => v
}

answered Jun 27, 2022 at 8:01

Guru Stron

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2 Comments

helloworld Over a year ago

thanks, but another silly question: what can I use as a default value and how to implement that? :)

Guru Stron Over a year ago

@helloworld it depends on your logic and what are you trying to achieve.

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