Scala match/case multiple typed branch - scala

Question

I will try to be as clear as possible.
I have this class that combines two other classes HBaseCREvent and HBaseCR:
class HBaseCREvent(val rowKey : scala.Predef.String, val actualEnd : scala.Predef.String, val actualImpact : scala.Predef.String, val actualStart : scala.Predef.String)
class combinedType[T]
object combinedType {
implicit object HBaseCREventWitness extends combinedType[HBaseCREvent]
implicit object HBaseCRWitness extends combinedType[HBaseCR]
}
and I have a method to implement like this
def convertHBaseObj[T:combinedType](event: T) : CRInput = {
event match {
case t # (_: HBaseCREvent | _: HBaseCR) => {
this.setActualEnd(t.actualEnd)
this.setActualImpact(t.actualImpact)
this.setActualStart(t.actualStart)
}
}
}
I am trying to avoid repeating the same set of statements when the input is of type HBaseCREvent or HBaseCR.
However, this approach does not work. My IDE cannot resolve the attributes (t.actualEnd, t.actualImpact, etc).
I have also tried this:
def convertHBaseObj[T:combinedType](event: T) : CRInput = {
event match {
case t: HBaseCREvent|HBaseCR => {
this.setActualEnd(t.actualEnd)
this.setActualImpact(t.actualImpact)
this.setActualStart(t.actualStart)
}
}
}
but I got an error:
illegal variable in pattern alternative
Any help on this?
Thanks

Answer 1

If you have control of HBaseCREvent, HBaseCR then extract your methods into a trait and implement that.
trait MyTrait {
def actualEnd = ???
def actualImpact = ???
def actualEnd = ???
}
def convertHBaseObj(t: MyTrait) = {
setActualEnd(t.actualEnd)
setActualImpact(t.actualImpact)
setActualStart(t.actualStart)
}
If you don't have control then you could do something like the following. I am re-using CombinedEvent here because your version doesn't do anything.
trait CombinedType[T] {
def actualEnd = ???
def actualImpact = ???
def actualEnd = ???
}
implicit def HBaseCREvent2CombinedType(t: HBaseCREvent) = new CombinedType[HBaseCREvent] {
def actualEnd = t.actualEnd
def actualImpact = t.actualImpact
def actualEnd = t.actualEnd
}
implicit def HBaseCR2CombinedType(t: HBaseCR) = new CombinedType[HBaseCR] {
def actualEnd = t.actualEnd
def actualImpact = t.actualImpact
def actualEnd = t.actualEnd
}
def convertHBaseObj[T](event: T)(implicit combinedEvent: CombinedEvent[T]) = {
setActualEnd(combinedEvent.actualEnd)
setActualImpact(combinedEvent.actualImpact)
setActualStart(combinedEvent.actualStart)
}
Either solution is better than your pattern matching implementation because they will fail at compile time rather than at runtime if the wrong type is passed to convertHBaseObj