change return type of the superclass method

Question

Having a scala class

class JobsHistory extends mutable.HashSet[JobInstance] {

      /**
       * Filter only Map Reduce Jobs
       * @return
       */
      implicit def onlyMapReduce = this.filter((job) => job.mapTasksCount > 0 && job.reduceTasksCount > 0)

      /**
       * Filter only jobs with successful status
       * @return
       */
      implicit def onlySucceeded = this.filter((job) => job.status == "SUCCEEDED")
    }

I would like to be able to do type of a call

instances.onlyMapReduce.onlySucceeded

where instances is a JobsHistory type. The problem is that I call a filter which is coming from superclass and returns HashSet rather than JobsHistory, how can I ensure proper return type.

Answer 1

I would suggest just adding those methods to a Set using Pimp My Library pattern.

case class JobInstance(status: String, mapTasksCount: Int, reduceTasksCount: Int)

implicit class JobHistory(val jobs: Set[JobInstance]) extends AnyVal {
  def onlyMapReduce = jobs.filter((job) => job.mapTasksCount > 0 && job.reduceTasksCount > 0)

  def onlySucceeded = jobs.filter(_.status == "SUCCEEDED")
}

val set = Set(JobInstance("SUCCEEDED", 3, 3), JobInstance("SUCCEEDED", 0, 3), JobInstance("Failed", 3, 3))

set.onlyMapReduce.onlySucceeded
res3: scala.collection.immutable.Set[JobInstance] = Set(JobInstance(SUCCEEDED,3,3))

It would work the same with mutable Set as filter returns a new set no matter if it's mutable or not.