Scala functional programming and mutability

Question

Let's say I have the following code:

class Pet(name: String) {
  def getName: String = {
    name match {
      case "" => generateRandomName
      case _  => name
    }
  }
}

object Pet {
  def apply(name: String) = new Pet(name)
}

where creating a Pet with an empty name would create a Pet with a random name. How would I save the state of the newly generated random name, so calling this method twice would return the same name generated from the first call?

val pet = Pet("")

// Let's say this prints "bob"
println(pet.getName)

// I want this to still print "bob". This would generate a new random name because the state isn't saved from the previous call. 
println(pet.getName)

I'd like to avoid var because it's considered bad practice -- how do you go about doing something like this? Is the best way to create a new copy of the class? That doesn't seem very efficient to me

jwvh · Accepted Answer · 2021-02-24 00:27:45Z

3

Using a default value in the constructor, you can do something like this...

class Pet(name: String = generateRandomName) {
  def getName: String = name
}

Then when you do this...

val pet = new Pet()

...getName will always return the same generated name, but this...

val pet = new Pet("")

...will populate name as an empty String.

edited Feb 24, 2021 at 0:27

answered Feb 23, 2021 at 23:57

jwvh

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