Swift to Kotlin, manage immutable list

Question

I am trying to port an existing Swift code to Kotlin and I'd like to use best practice for the following Swift code:

struct Deck {

    private(set) var cards: [Card]

    var cardsCount: Int {
        return self.cards.count
    }

    init(cards: [Card] = []) {
        self.cards = cards
    }

    mutating func add(card: Card) {
        self.cards.append(card)
    }
}

The design goals are:

1. cards property is not modifiable outside of the class so its type should be List<Card>

2. fun add(card: Card) should modify the internal cards list

Is there a way to achieve this in Kotlin without using two separate properties - one private var mutableCards: MutableList<Card> and one computed property val cards: List<Card> get() = this.mutableCards

I need some best practice for such situation.

Answer 1

Since the read-only List is "under the hood" also a mutable list, you may want to leverage on casting to a MutableList, doing so:

class Card {
}

class Deck(cards:List<Card>){
    var cards:List<Card>

    init {
       this.cards = cards
    }

    public fun add(card:Card) {
      (cards as MutableList<Card>).add(card)
   }
}

fun main(args: Array<String>) {    
   var cards:List<Card> = arrayListOf()
   // here I can't modify cards
   var deck = Deck(cards)
   deck.add(Card())
   print(deck.cards.count()) // printing 1
}

to be able to test it, copy and paste here.