return-type-varies

  def doWork[A: Numeric, B: Numeric](values: Seq[Option[A]], op: String): Option[B] = {
    import spire.implicits._
    val v = values.flatten
    if (v.isEmpty) {
      None
    } else {
      op match {
        case "sum" => Some(v.qsum) // returns A
        case "avg" | "avg" => Some(v.qsum / v.length) // returns Double
        case "max" => Some(v.qmin) // A
        case "min" => Some(v.qmin) // A
        case _ => None
      }
    }
  }
  
  val resultA = doWork(Seq(Some(44L),Some(34L),Some(45L),None,Some(34L)),"sum")
  val reulltB = doWork(Seq(Some(44L),Some(34L),Some(45L),None,Some(34L)),"avg")