why Partial function in scala is giving run time error for input 0?

Question

I am expecting my partial function to discard for input 0 , but instead it is giving match error . Will you please explain exactly why is it happening? What I am missing?

object PartialFunction extends App {

  val divider : PartialFunction[Int,Int] = {
    case d : Int if d != 0 => 42/d
  }
  println(divider(0))
  //println(fraction(0))
}

What is your expected output? How could the compiler know what to do with that divider(0) call? You should wrap it with a if (divider.isDefinedAt(0)) — Luka Jacobowitz
– Luka Jacobowitz, Commented Jan 11, 2017 at 14:22

Nagarjuna Pamu · Accepted Answer · 2017-01-11 14:38:35Z

3

You did not tell what to do when the input is 0. 0 does not match the case where because of the guard d != 0

Change your implementation to accommodate 0 case

  val divider : PartialFunction[Int,Int] = {
    case d : Int if d != 0 => 42/d
    case 0 => 0 //return some integer
  }

answered Jan 11, 2017 at 14:38

Nagarjuna Pamu

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1 Comment

Priyaranjan Swain Over a year ago

Thank you , I was thinking as case is matching for any integer , why it shows match error for 0 , but yeah now I am pretty clear , it's guard which is preventing to evaluate 0, so it's kind of nomatch for 0 .

Shankar · Accepted Answer · 2017-01-11 16:18:11Z

1

Or you can define what's the default case.

val divider : PartialFunction[Int,Int] = {
    case d : Int if d != 0 => 42/d
    case _ => 0
  }

answered Jan 11, 2017 at 16:18

Shankar

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