Styjun

I have to retrieve Derived class objects stored in a Map given the respective class name as key.

As show below

trait Caluclator
class PreScoreCalculator(data:Seq[Int]) extends Caluclator
class BenchMarkCalculator(data:Seq[Int]) extends Caluclator


val calculatorsLookUp:Map[String, Calculator] = Map[String, Calculator](
 "PreScore" -> new PreScoreCalculator,
 "BenchMark" -> new BenchMarkCalculator
 )

Given key name i need to get respective object/instance from Map

def getCalculatorByOperationName(operation:String) : Option[ Calculator] = 
 calculatorsLookUp.get(operation)
 

I am calling as below

 val calcName = "PreScore"

 val opt = getCalculatorByOperationName(calcName) 

 if(opt.isInstanceOf[PreScoreCalculator] ) /// this is coming as false
 calculationController.calculate(opt) // this is not being executed.

Expect :
Execute calculationController.calculate(opt)

Error :
Above if condition is false hence not getting executed.

So how to handle this problem?

How to handle below i.e. default constructor objects ?

class PreScoreCalculator(data:Seq[Int]) extends Caluclator

You should not call isInstanceOf & asInstanceOf manually, because that is basically throwing the compiler away.

You should use pattern matching instead:

opt match 
 case Some(c: PreScoreCalculator) => calculationController.calculate(c)
 ... // Other calculators.
 case None => println("Calculator not found.")

Note: This is basically the same Ichoran and I already said in gitter, I am just leaving this here for the record.

You have a small bug:

opt is of type Option[Calculator]

In Scala a nice way to handle that is pattern matching:

opt match 
 case Some(calculator: PreScoreCalculator) =>
 calculationController.calculate(calculator)
 case _ => // nothing to do
 

Or do it in a more declarative way:

 opt.filter(_.isInstanceOf[PreScoreCalculator])
 .foreach(calculationController.calculate)

However the use of instanceOf is a bit of an anti pattern.

As a tip:

Use println(opt.getClass) > then you see the class.

The problem here is on

val opt = getCalculatorByOperationName(calcName)

because it will return Option[Calculator] not Calculator. Now it will look like this..

if(opt.map(_.isInstanceOf[PreScoreCalculator]).getOrElse(false))
 calculationController.calculate(opt.get)

Hope it helps.