scala's Try elegant on error behavior

Question

Is there a more elegant way of doing this in scala?

def doTheDangerousThing(): Try[Result] = {
  val result = Try(dangerousOp)

  if (result.isFailure) {
     println("error")
  }

  result
}

Answer 1

I think your if statement is perfectly valid. Here is another alternative:

def doTheDangerousThing(): Try[Result] = Try(dangerousOp) recoverWith {
    case exception => println("error"); Failure(exception)
}

Answer 2

Something like this:

   def doTheDangerousThing[Result](dangerousOp: =>Result): Try[Result] = Try(dangerousOp) match {
    case o @ Failure(_) =>  println("error"); o
    case _ => _
  }

Answer 3

Not sure if this is more idiomatic, but sometimes I find that placing the recoverWith in this manner improves readability for me:

def doDangerousThing(): Try[Result] = Try {
  dangerousOp
} recoverWith {
  case t: Throwable => println("error"); Failure(t)
}

Answer 4

My preferred,

def doTheDangerousThing(): Option[Result] = Try (dangerousOp) toOption

If the Try is successful you will get a Some(value) , if it fails a None .

For a large compilation on Try uses, have a look at Try introduced in Scala 2.10.0 .

Answer 5

There are ways. For instance:

def doTheDangerousThing(): Try[Result] = {
  val result = Try(dangerousOp)

  result.failed foreach { _ =>
     println("error")
  }

  result
}

Or, if you don't want to repeat result all through, then:

def doTheDangerousThing(): Try[Result] = {
  Try(dangerousOp) recover {
    case ex => println("error"); throw ex
  }
}

Answer 6

In some cases I love to use two-step approach which will allow me a more granular error message control:

  def retrieveData(dataId: String): Try[String] = {
    Try {
      Option(someApi(dataId))
        .getOrElse(throw SomeApiFailedException("invalid dataId"))
    } recoverWith {
      case e: SomeApiFailedException => Failure(e)
      case e: Throwable => Failure(SomeApiFailedException("failed retrieve dataId"))
    }
  }

  case class SomeApiFailedException(err: String) extends RuntimeException(err)

Answer 7

Well, I suppose you could do something like this:

def doTheDangerousThing(): Option[Result] = 
  Try(dangerousOp) match {
    case Success(result) => Some(result)
    case Failure(e) => None //might want to log the error as well
  }

Answer 8

I could choose from either of the three implementations, depending on whether I want to:

• Simply propagate it upwards ( doTheDangerousThing1 )
• Ignore the error ( doTheDangerousThing2 )
• Intercept the error while propagating it upwards ( doTheDangerousThing3 )

Here is the code:

import scala.util.{Try,Success,Failure}
object temp {
  type Result = Int

  def dangerousOp = {
    val r = scala.util.Random.nextInt(10)
    if (r > 5) r else throw new RuntimeException("Failed on " + r)
  }
  def logMessage[T](t: T) = println(t)

  def doTheDangerousThing1(): Try[Result] = Try(dangerousOp)

  def doTheDangerousThing2(): Option[Result] = {
    Try(dangerousOp) match {
      case Success(r) => Option(r)
      case _ => None
    }
  }


  def doTheDangerousThing3(): Try[Result] = {
    Try(dangerousOp) match {
      case t @ Success(r) => t
      case t @ _ => logMessage("failed: "+t); t
    }
  }
}

Inside the REPL

scala> doTheDangerousThing1
res0: scala.util.Try[Result] = Success(9)

scala> doTheDangerousThing1
res1: scala.util.Try[Result] = Success(9)

scala> doTheDangerousThing2
res2: Option[Result] = None

scala> doTheDangerousThing2
res3: Option[Result] = Some(7)

scala> doTheDangerousThing3
failed: Failure(java.lang.RuntimeException: Failed on 0)
res4: scala.util.Try[Result] = Failure(java.lang.RuntimeException: Failed on 0)

scala> doTheDangerousThing3
failed: Failure(java.lang.RuntimeException: Failed on 0)
res5: scala.util.Try[Result] = Failure(java.lang.RuntimeException: Failed on 0)