Return same value for multiple exceptions - scala

Question

Given a block that catches more than one exception is it possible to handle multiple exceptions without putting the desired value in every case block? e.g. it would be nice if something like this worked:
val foo: Int = try {
//do stuff that results in an Int
} catch {
case e: SomeException => //do something if this gets thrown
case e: SomeOtherException => //do something different if this gets thrown
0
}
But that results in a compile error (type mismatch; found : Unit required: Int). I could put the default in each throwable case e: SomeException => {/*do something if this gets thrown*/; 0} - but that just seems like code smell so I'm hoping there is a more elegant solution.

Answer 1

You could simply wrap the exception handling:
val foo: Int = try {
//do stuff that results in an Int
17
} catch { case t: Throwable => t match {
case e: SomeException => //do something if this gets thrown
case e: SomeOtherException => //do something different if this gets thrown
}
42
}

Answer 2

You can take advantage of partial functions to do your error handling using the built in Try
val foo: Int ={
val value = Try{
//stuff
}
unwrap(0, value){
case x: SomeException => doStuff()
case x: OtherExcetion => doMoreStuff()
}
}
def unwrap[A](ret: A, value: Try[A])(f: Failure[A] => Unit): A = value match{
case Success(x) => x
case x: Failure => f(x); ret
}
and voila, you've handled it quite well.

Answer 3

The catch keyword expects a PartialFunction, which can easily be chained with andThen:
scala> val pf1: PartialFunction[Throwable, Unit] = { case _: IllegalArgumentException => println("pf1") }
pf1: PartialFunction[Throwable,Unit] = <function1>
scala> val pf2: PartialFunction[Unit, Int] = { case _ => println("pf2"); 0}
pf2: PartialFunction[Unit,Int] = <function1>
scala> try throw new IllegalArgumentException catch pf1 andThen pf2
pf1
pf2
res0: Int = 0
scala> try throw new NoSuchElementException catch pf1 andThen pf2
java.util.NoSuchElementException
The second PartialFunction is only executed when the first one matched its argument, which can be a problem when you want to catch other exceptions (that also should not return the default value). But for this case, there is orElse:
scala> val pf3: PartialFunction[Throwable, Int] = { case _ => println("pf3"); 1}
pf3: PartialFunction[Throwable,Int] = <function1>
scala> try throw new NoSuchElementException catch pf1 andThen pf2 orElse pf3
pf3
res2: Int = 1

Answer 4

You can use the Try object to wrap your possibly failing code, and then compose the outcome like this
val foo: Int = (Try {
//do stuff that results in an Int
} recover {
//here we handle the recovering
handleFail andThen defaultInt
}).get
val handleFail: PartialFunction[Throwable, Unit] = {
case e: SomeException => //do something if this gets thrown
case e: SomeOtherException => //do something different if this gets thrown
val defaultInt: PartialFunction[Unit, Int] = { case _ => 0 }