Type Object does not support slicing Unity3D

Question

I am getting the following error in my code and I can't seem to understand why. Can anyone help me with it?

This is my current code. The line causing the error is marked in a comment near the end.

var rows : int = 4;
var cols : int = 4;
var totalCards : int = cols * rows;
var matchesNeedToWin : int = totalCards * 0.5; 
var matchesMade : int = 0;

var cardW : int = 100;
var cardH : int = 100;

var aCards : Array; 
var aGrid : Array;

// This Array will store the two cards that the player flipped
var aCardsFlipped : ArrayList; 

// To prevent player from clicking buttons when we don't want him to
var playerCanClick : boolean; 

var playerHasWon : boolean = false;     


class Card extends System.Object {
var isFaceUp : boolean = false;
var isMatched : boolean = false;
var img : String;

    function Card () {
        img = "robot";
    }
}

function Start () {

    var i : int = 0;
    var j : int = 0;

    playerCanClick = true;
    aCards = new Array ();
    aGrid = new Array ();
    aCardsFlipped = new ArrayList ();

    for ( i = 0; i < rows; i++) {
        aGrid [i] = new Array ();

            for (j = 0; j < cols; cols++ ) {
            aGrid [i] [j] = new Card (); // <------ Error over here
        }
    }
}


function Update () {
    Debug.Log("Game Screen has loaded");
}

The error states as follows:

Error BCE0048: Type 'Object' does not support slicing. (BCE0048) (Assembly-UnityScript)

Answer 1

Use Unity's multidimensional arrays rather than jagged arrays, in which this appears to be an unsolved problem. According to this Unity question, you can declare them like this:

var a : float[,];

Or in your case, I'm guessing the syntax would be this (with or without the new, I'm not sure):

aGrid = new Card[,];

So instead of your problematic line you'd have this:

aGrid[i,j] = new Card();

If you really do want to use a jagged array you need to use a workaround (according to that first link): use the Array.Add() method rather than directly setting the variable at each index.

Answer 2

Like Jonathan Hobbs said, I've made a few changes.
This is what I modified those code

var aCards:Array
var aGrid:Card[,]; //<-- change how you declare this variable to multidimensional arrays
var aCardsFlipped:ArrayList;

And change this in the Start function

function Start () {
    playerCanClick = true; 
    aCards = new Array();
    aGrid = new Card[rows,cols]; //<-- I instantiate it as rows*cols array
    aCardsFlipped = new ArrayList();
    for (var i=0;i<rows;i++)
    {
        for (var j=0;j<cols;j++)
        {
            aGrid[i,j] = new Card(); //<-- Then assign the value like this
        }
    }
}

Hope this help