Scala, default code for PartialFunction? - scala

Question

I am using Akka and would like to run some code for all cases of a PartialFunction. For actor supervision, I have something like:
val supervisorStrategy = OneForOneStrategy() {
case npe: NullPointerException => Stop
case re: RuntimeException => Restart
}
The only way I have found to run some code for all cases without having to write it again at every case, is:
val pf = new PartialFunction[Throwable, Directive] {
def apply(throwable: Throwable) = {
doSomething(throwable)
throwable match {
case NullPointerException => Stop
case RuntimeException => Restart
}
}
def isDefinedAt(throwable: Throwable) = true
}
val supervisorStrategy = OneForOneStrategy()(pf)
I have looked around and to other answers (like this one) but couldn't figure out any alternative way to the one I came up with.

Answer 1

Doesn't seem Akka-specific. You can always combine any two functions using andThen. Specifically:
package com.example
import akka.actor.OneForOneStrategy
import akka.actor.SupervisorStrategy.{Decider, Restart, Stop}
object Answer extends App {
val doSomething:PartialFunction[Throwable, Throwable] = { case e =>
println(s"doing something with $e")
e
}
val decide:Decider = {
case _:NullPointerException => Stop
case _:RuntimeException => Restart
}
val strategy = OneForOneStrategy()(doSomething andThen decide)
val errors = Seq(new NullPointerException, new RuntimeException)
errors map strategy.decider foreach println
}
More generally:
package com.example
object Answer extends App {
val inspect:PartialFunction[Throwable, Throwable] = { case e =>
println(s"inspecting $e")
e
}
val decide:PartialFunction[Throwable, String] = {
case npe:NullPointerException => "NPE!"
case iae:IllegalArgumentException => "Bad arg!"
}
val combined = inspect andThen decide
val errors = Seq(new NullPointerException, new IllegalArgumentException)
errors map combined foreach println
}

Answer 2

This should do it :
val supervisorStrategy = OneForOneStrategy() {
case x =>
doSomething(x)
x match {
case npe: NullPointerException => Stop
case re: RuntimeException => Restart
}
}

Answer 3

Thanks for the other answers, but in this Akka specific situation I can't get them to work. For instance, this won't compile:
val ft = OneForOneStrategy() { x: Throwable =>
doSomething(x)
x match {
case npe: NullPointerException => Stop
case re: RuntimeException => Stop
}
}
Error:(48, 47) type mismatch;
found : Throwable => akka.actor.SupervisorStrategy.Directive
required: akka.actor.SupervisorStrategy.Decider (which expands to) PartialFunction[Throwable,akka.actor.SupervisorStrategy.Directive]
I am using Akka 2.4.11 and Scala 2.11.8
The only working solution for me was the way I described in the initial question.