Question

Trying to find a valid and flexible way to store a sequence of class types in Scala that I can later use to spin up new instances of that type:

class Event(

  val name: String,
  val channels: Seq[String],
  val processors: Seq[T] // a sequence of processor classes

)

Each processor in the sequence above is an Akka Actor class. I plan on creating a new Actor every time data is received by mapping out the processors like so:

event.processors.foreach { processorType =>
  val processor = newProcessor(processorType) // does all the Akka creation stuff
  processor ! Data
}

Update: apparently the above is rather correct, so how do we enforce that Seq[T] is processor-types only? So sticking in classes like class Calculator extends Processor

My guess is that there are some gotchas with Scala that I missed, so thanks for your help.

Answer 1

Seq[T] would only be valid if there is either a type T or a type parameter.

scala> class Event(val seq:Seq[T])
<console>:7: error: not found: type T
       class Event(val seq:Seq[T])
                               ^

To have a list of classes it has to be of a Seq[Class[_]].

Let’s suppose the processors you mention are of type Processor. A smaller illustrative example:

scala>  trait Processor; class P1 extends Processor; class P2 extends Processor

scala> case class Event(val seq:Seq[Class[_ <: Processor]])
defined class Event

scala> Event(List(classOf[P1],classOf[P2]))
res4: Event = Event(List(class P1, class P2))

scala> res4.seq map { _.newInstance }
res6: Seq[Processor] = List(P1@43655bee, P2@337688d3)