Question

Assuming that I have a Scala case class like the following:

case class Item(
  roundedValue: Double = 0.00)

I want to perform the following rounding operation on roundedValue every time the variable is updated:

roundedValue = math.round(roundedValue*100)*0.01

In other languages I would just override the setter for roundedValue, but it appears that I cannot override the setter for a case class variable or it won’t compile.

One solution I have seen is to rename roundedValue to _roundedValue and make it private, and then add public methods to simulate getter and setter (with rounding logic): Overriding setter on var

However this makes constructor usage pretty awkward for the case class when using named parameters. Is there any other way to do this, or is this a limitation of case classes in Scala?

Answer 1

If you can make it work, I would recommend keeping your case class immutable, but making a “copy” method that does your mutations on a new instance.

case class Item(roundedValue: Double = 0.0) {
  def withValue(newValue: Double) = Item(math.round(newValue*100)*0.01)
}

You may also/instead want to have a similar method in the companion object:

object Item {
  def withValue(value: Double) = Item(math.round(roundedValue*100)*0.01)
}