Type mismatch error in recursive function in scala

Question

I have the following recursive call written in Scala:

  def calculateFingerPrint(t: Tree):Int =
{
  if(t.isInstanceOf[Leaf])
    calculateIDS(t).hashCode()

  else if(t.isInstanceOf[OtherNode])
    //error --> calculateIDS(t).concat(calculateFingerPrint(t.children.head).toString()).hashCode 

}

 def calculateIDS(t: Tree):String= {
//returns some string
}

The commented line is throwing type mismatch error and saying Found: Anyval Required:Int.

Can anyone please tell what is the problem here?

Could you please share all the code necessary to reproduce the problem? - BTW, you should not call isInstanceOf in Scala, we have better tools like pattern matching for that. — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Dec 5, 2019 at 16:43

Tim · Accepted Answer · 2019-12-05 16:49:35Z

2

You need a final else clause to return the default value if t is not Leaf or OtherNode.

A match expression would be better than using isInstanceOf calls.

answered Dec 5, 2019 at 16:49

Tim

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2 Comments

A Beginner Over a year ago

So, scala will throw error if there is no final else statement unlike Java where you could write this same code without specifying a final else.

Suma Over a year ago

It will not throw an error, the problem is type of if without else is Unit (type of if with else is a common super-type of both possible results).

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