Updating element property in scala list buffer

Question

I have a listbuffer of events Animals. I am trying to update one of those properties.However, when using update it updates the whole element. Is there a way to update a particualr property? I'd want to update the owner for example.

import java.util.UUID

case class Car(model: String, owner: String)

var cars = new scala.collection.mutable.ListBuffer[Car]()

var car1 = Car("honda", "John")
var car2 = Car("chevy", "Xavier")
var car3 = Car("subaru", "Mario")

cars += car1
cars += car2
cars += car3

def generateRandomGuid(numOfTenants: Int) = {
  List.tabulate(numOfTenants)(_ => UUID.randomUUID().toString())
}

val ownerList = generateRandomGuid(3)

for(newowner <- ownerList) {
    for(eventIdx <- 0 to cars.length-1) {
      //cars.update(eventIdx, newowner)
     cars(eventIdx).owner = newowner 
    }  
}

Update1: updated to using var for the different cars and the list buffer to Car however, i still cannot reassign because error: reassignment to val cars(eventIdx).owner = newowner

To update a particular field, you don't have to do anything to your ListBuffer (which should be a ListBuffer[Car], btw). You'd have to mark owner with var, and then you can do cars(eventIdx).owner = newOwner — user
– user, Commented Nov 4, 2020 at 21:30
After updating that, as well as using 'var' I still cannot update the field because of reassignment to val — nrvaller
– nrvaller, Commented Nov 4, 2020 at 21:49

tantalum · Accepted Answer · 2020-11-05 14:21:04Z

2

The short answer is that objects in Scala are immutable by default. The error you are getting (error: reassignment to val cars(eventIdx).owner = newowner) means that you cannot update the owner property of a car, because properties are immutable by default. As @nrvaller mentioned in their comment, you can declare the owner property as a variable.

edited Nov 5, 2020 at 14:21

answered Nov 4, 2020 at 21:59

tantalum

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1 Comment

user Over a year ago

I think you meant "immutable" instead of "constants" (and you did use "immutable" the first time)

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