CODEWITHSUNDEEP
scala
Wolfgang Liebich
Wolfgang Liebich

Reputation: 408

How can I call a super class method from a code block in a derived class?

This question is somewhat hard to summarize. Following code block shows what I want to do. I have a base class like this:

 `class Base {
   def methA:String="ook"
   def methB:Int=1
}

Also I have a derived class, where I want each subclass method to call the super class method twice, compare the results and throw an exception on mismatch (this is for a test scenario).

But if I write 

class Derived extends Base {

  private def callDoublyAndCompare[T](fun:()=>T) : T = {
      val fst=fun()
      val snd=fun()
      if(fst!=snd) throw new RuntimeException(s"Mismatch fst=$fst != snd=$snd")
      snd
  }

  override def methB:Int={
     callDoublyAndCompare(() => super[Derived].methB)
  }
}

Then this will not compile. The only way out of this problem sofar has been to extract a method in class Derived which only calls the superclass' methB and to call this from the lambda call.

Is there a better way?

Upvotes: 0

Views: 42

Answers (2)

Wolfgang Liebich
Wolfgang Liebich

Reputation: 408

The original example was not fully complete insofar as the Derived class was defined as inner class of another scala class. After I moved out this inner class to the top level, the example from Praveen above suddenly worked.

Upvotes: 0

Praveen L
Praveen L

Reputation: 987

I understood you want to call super call method. Hope below is what you want.

You can call that as below with the key word super only

(new Derived).methB . This will call super call method in callDoublyAndCompare twice as per your code . 

class Derived extends Base {

  private def callDoublyAndCompare[T](fun:()=>T) : T = {
      val fst=fun()
      val snd=fun()
      if(fst!=snd) throw new RuntimeException(s"Mismatch fst=$fst != snd=$snd")
      snd
  }

  override def methB:Int={
     callDoublyAndCompare(() => super.methB) //kept only super
  }
}

Upvotes: 1

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