How to create partial function from runtime value in Scala

Question

I'm trying to create partial function from runtime value and combine partial functions after that like this:

class Test(val function: PartialFunction[Int, Boolean]) {
  def add(v: Int): Test = {
    new Test(function.orElse{case v => true})
  }
  def contains(v: Int) = function.isDefinedAt(v)
}

val test: Test = new Test({case 1 => true})
val test2 = test.add(2)
println(test2.contains(1))
println(test2.contains(2))
println(test2.contains(3))

This code prints

true
true
true

But the last line should be false. Why is this so? What I'm doing wrong?

Tim · Accepted Answer · 2020-03-20 12:34:44Z

5

{ case v => true } is always a match. You want to test the value of v:

  new Test(function.orElse{case `v` => true})

edited Mar 20, 2020 at 12:34

answered Mar 20, 2020 at 10:14

Tim

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2 Comments

sergeda Over a year ago

Can you, please, provide more info about cases when isDefinedAt can return true even if the function will fail?

Tim Over a year ago

I have re-checked the documentation and I was wrong about this. isDefinedAt does accurately indicate whether a value is handled by the partial function or not. So your code is good to go, and apologies for confusing things.

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