How to manage Lists with Future in dart? - dart

Question

I am new at Dart; and, I created a List of playing card objects called Deck. I am trying to select a random card, then remove the card from the deck. I am getting duplicates, as it appears subsequent cards are picked before the deck is reduced. How would I handle a future chain of events that will pick 10 unique random cards from the deck?
class Card{
String face;
String suit;
String rank;
String imgSrc;
String holdImgSrc;
Card(
this.face,
this.suit,
this.rank,
this.imgSrc,
this.holdImgSrc
);
}
import 'dart:math' show Random;
Random indexGen = new Random();
getCard1(){
card1 = deck[indexGen.nextInt(deck.length)];
deck.removeWhere((item) => item == card1);
return card1;
}
getCard2(){
card2 = deck[indexGen.nextInt(deck.length)];
deck.removeWhere((item) => item == card2);
return card2;
}
When I try to return a Card Object as a future I get:
new Future((getCard1()))
.then((getCard2()))
.then((getCard3()));
type 'Card' is not a subtype of type '() => dynamic' of 'computation'.
When I try to return the deck List I get:
type 'List' is not a subtype of type '() => dynamic' of 'computation'.
Am i missing the right syntax, flaw in my logic, or do I need to handle the list differently, by maybe watching for changes?
edit to add: The futures syntax works, however, the deletes do not appear to be happening correctly.
I changed the code, to the code suggested by Jim-Y below, except for preloading new Card objects from a List using the second named constructor. The amended code and printout is as follows:
fullDeck[
...
var tenC = new Card.full(17,'10_of_clubs','c','10','10_of_clubs.png','10_of_clubs_h.png');
var tenD = new Card.full(18,'10_of_diamonds','d','10','10_of_diamonds.png','10_of_diamonds_h.png');
var tenS = new Card.full(19,'10_of_spades','s','10','10_of_spades.png','10_of_spades_h.png');
var tenH = new Card.full(20,'10_of_clubs','c','10','10_of_clubs.png','10_of_clubs_h.png');
...]
Deck<Card> deck = new Deck<Card>();
Random indexGen = new Random();
for(var c = 0; c < 20; ++c) {
var card = new Card(c);
deck.add(fullDeck[c]);//List of 52 full card objects
}
for(var i = 0; i < 10; ++i) {
var rnd = indexGen.nextInt(deck.size());
print('${deck.get(rnd).face} Deck size: ${deck.size()}');
}
}
4_of_clubs Deck size: 19
10_of_diamonds Deck size: 18
5_of_clubs Deck size: 17
4_of_spades Deck size: 16
5_of_spades Deck size: 15
10_of_clubs Deck size: 14
10_of_clubs Deck size: 13
3_of_spades Deck size: 12
5_of_diamonds Deck size: 11
3_of_diamonds Deck size: 10
As you can see the 10 of Clubs is printed twice. So, If the 10 was removed in pass 6, why is it still there in pass 7?

Answer 1

If you want to chain the calls this way the methods must return a future:
Caution: I have not tested the code:
// I don't see what type 'Card' actually is from your code
Future<Card> getCard1(){
return new Future(() {
card1 = deck[indexGen.nextInt(deck.length)];
deck.removeWhere((item) => item == card1);
return card1;
});
}
the same for getCard2()
Future<Card> getCard2(){
return new Future(() {
card2 = deck[indexGen.nextInt(deck.length)];
deck.removeWhere((item) => item == card2);
return card2;
});
}
you call it with
getCard1().then((c) => getCard2()).then((c) => print(c));
as getCard1 and getCard2 are essentially the same methods you could combine them to one
List<Card> cards = [];
Future<Card> getCard(int i){
return new Future(() {
cards[i] = deck[indexGen.nextInt(deck.length)]; // not clear what card is
deck.removeWhere((item) => item == card[i]);
return card[i];
});
}
.
getCard(1).then((c) => getCard(2)).then((c) => print(c));

Answer 2

I can't see now why you need to use Futures for this. In the following code, i will try to address a possibly better approach of removing a Card from a deck using Dart's generic features :)
Your original Card class, I extended it for demonstrational purpose:
class Card {
int id;
String face;
String suit;
String rank;
String imgSrc;
String holdImgSrc;
Card(this.id);
Card.full(this.id, this.face, this.suit, this.rank, this.imgSrc, this.holdImgSrc);
}
Then, you could make a generic container for your cards instead of using a simple List.
class Deck<T extends Card> {
List<T> _container = new List<T>();
T get(int index) => _container.removeAt(index);
void add(T item) => _container.add(item);
int size() => _container.length;
}
This would make your example easier to extend later, and you gain much expression power with it.
Then, you could write something like this, to remove 10 random elements from the deck.
void main() {
Deck<Card> deck = new Deck<Card>();
Random indexGen = new Random();
for(var c = 0; c < 20; ++c) {
var card = new Card(c);
deck.add(card);
}
for(var i = 0; i < 10; ++i) {
var rnd = indexGen.nextInt(deck.size());
print('${deck.get(rnd).id} Deck size: ${deck.size()}');
}
}
On this simple example, with these simple card objects there are no duplicates. However, if you need to, you could extend your Deck class with a(n) fGet method what could be a method returning a Future as mentioned before by #Günter.
I hope i gave you some good ideas :)
Cheers