Multidimensional array of objects bug in swift?

Question

I have a multidimensional (2D) array of items (object) and I decided to use the "natural" way to create it (so instead of using the trick to transform a 1D array into 2D, I go 2D directly).

An item has a X & Y position on the matrice and the item has also a random type.

Everything seems to work except for the Y position of all the items... Because of how Swift handles 2D, I needed to initialize the 2D array then affect the values correctly to each item.

I do verify the value that I affect to the items, they work. Then when I verify the item after it has been correctly set, the Y position is like unique to all the items.

class Matrix {
    var nbCol: Int
    var nbRow: Int
    var items: [[Item]]

    init(nbCol: Int, nbRow: Int) {
        self.nbCol = nbCol
        self.nbRow = nbRow
        items = Array<Array<Item>>()
        //Initialize
        for col in 0..<Int(nbCol) {
            items.append(Array(count: nbRow, repeatedValue: Item()))
        }
        //Affect the correct values to each item
        createItems()
    }

    func createItems() {
        //Assign X, Y & type values to the item
        for x in 0..<Int(nbCol) {
            for y in 0..<Int(nbRow) {
                items[x][y].setItem(x, y: y, type: ItemType.random())
                println("Create for (\(x), \(y)): (\(items[x][y].x), \(items[x][y].y))")
            }
        }
        //Verify the values
        for x in 0..<Int(nbCol) {
            for y in 0..<Int(nbRow) {
                println("Check for (\(x), \(y)): (\(items[x][y].x), \(items[x][y].y))")
            }
        }
    }
}

And Item (part of it) is :

class Item: Printable {
    var x: Int
    var y: Int
    var type: ItemType  //Enum

    func setItem(x: Int, y: Int, type: ItemType) {
        self.x = x
        self.y = y
        self.type = type
    }

}

And the output (with the problem in red):

Console output

As you can see, during "setting values", X & Y are correct. But at check, only X is correct and Y is "stuck". Am I doing something wrong ?

EDIT : By the way, all items has also the same type. Only X is correct, Y & type are "fixed" for all items.

[In reply to "Can we have the full code"] Sure thing : gist.github.com/BabyAzerty/4e4aaa3cae6838f4b050 But I believe @Paulw11 pointed out the problem, yet I don't know how to code a solution for it. — Kalzem
– Kalzem, Commented Dec 1, 2014 at 23:54

Paulw11 · Accepted Answer · 2014-12-01 23:58:02Z

1

Your problem is that repeatedValue:Item() is only evaluated once, it is not evaluated count times. This means that you have the same Item in each row of a given column, so when you set the values you are overwriting the previous one - which is why you get the last value (2) when you print it.

You need to use a loop to populate the rows rather than using the count/repeatedValue construct.

init(nbCol: Int, nbRow: Int) {
    self.nbCol = nbCol
    self.nbRow = nbRow
    items = Array<Array>()
    //Initialize
    for col in 0..<Int(nbCol) {

         var colArray=Array<Item>()

          for row in 0..<Int(nbRow) {
             colArray.append(Item())
          }

        items.append(colArray)
    }
    //Affect the correct values to each item
    createItems()
}

edited Dec 1, 2014 at 23:58

answered Dec 1, 2014 at 23:43

Paulw11

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1 Comment

Kalzem Over a year ago

Oh I understand the problem ! But how should I proceed a loop for the rows in swift ? I tried to do it as anyone would do it in C/C++, but in Swift, you can't create an array with, let's say, 12 fixed rows. And I can't put nil instead of Item() in the repeatedValue

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