Swift Array handling of Subclasses - objective-c

Question

If I have a variable declared like var gameBoard: [Piece] = [], is there any way to add a subclass of Piece, called Queen, to the array?
I am using Piece to represent all pieces. Queen, Pawn, Bishop and such are all subclasses of Piece, and should be included on the board.
I remember doing this frequently in Objective C, where subclasses were able to be used in place of the superclass. But in my first attempts, it I am getting an error saying
'#lvalue $T11' is not identical to 'Piece`
Is this not possible anymore? Or would there need to be some use of generics that I cannot think of right now?
Edit
Here is the implementation of my board, including only the relevant parts.
struct GameBoard{
var board: [[Piece]]
init() {
board = []
for _ in 0...7{
var collumn: [Piece] = []
for _ in 0...7{
var piece = Piece(player: .None, board: self)
collumn.append(piece)
}
board.append(collumn)
}
}
subscript(coords:(Int, Int) ) -> Piece {
return board[coords.1][coords.0]
}
}
The code that fails is
var board = GameBoard()
var q = Queen(player: .Black, board: board)
board[(4,5)] = q //Throws the error
board.board[5][4] = q //Works
It seems to me that these two should work the same way. It may be an issue with the subscripting, but I am not completely sure.

Answer 1

Just to followup on your edits, this works fine in Swift. For example:
class Piece {}
class Bishop : Piece {}
let pieces: [Piece] = [Bishop()]
Do you have an example that does not work?
As a note, when you see #lvalue $T## in your errors, it often means you're trying to modify a constant. An easy way to make that mistake is to try to modify an array that was passed to you and that you did not mark var. For example, see Swift function that takes in array giving error: '#lvalue $T24' is not identical to 'CGFloat'.

Answer 2

Here is how I would write it. Includes answer to the question about subscripting, and for bonus, uses a Coords struct in place of tuples (allows implementation of Printable for example) and uses optionals for each square (allows nil to be used as the representation of an empty square.)
class Piece : Printable {
var description: String { get { return "Piece" } }
}
class Queen : Piece {
override var description: String { get { return "Queen" } }
}
struct Coords : Printable {
let column: Int
let row: Int
init(_ column: Int, _ row: Int) {
self.column = column
self.row = row
}
var description: String { get { return "Coords(\(column), \(row))" } }
}
struct GameBoard {
var board: [[Piece?]]
init() {
board = []
for _ in 1...8 {
board.append(Array<Piece?>(count: 8, repeatedValue:nil))
}
}
subscript(c: Coords) -> Piece? {
get {
return board[c.column][c.row]
}
set (newValue) {
board[c.column][c.row] = newValue
}
}
}
func testGameBoard() {
var board = GameBoard()
board[Coords(4, 5)] = Queen()
func printSquare(coords: Coords) {
if let p = board[coords] {
println("At \(coords) is a \(p)")
} else {
println("At \(coords) is an empty square")
}
}
printSquare(Coords(4, 5)) // Prints: At Coords(4, 5) is a Queen
printSquare(Coords(4, 6)) // Prints: At Coords(4, 6) is an empty square
}

Answer 3

As long as Queen is a subclass of Piece then there would be no problem. As such:
class Piece {}
class Queen : Piece {}
class Board {
var board : [[Piece?]] =
{ var board : [[Piece?]] = []
for _ in 0..<8 { board.append (Array<Piece?>(count: 8, repeatedValue:nil)) }
return board } ()
subscript (row:Int, col:Int) -> Piece? {
get { return board[row][col] }
set { board[row][col] = newValue }}
}
and then use as:
23> let board = Board()
 24> b[0,4] = Queen()
 25> b[7,4] = Queen()
 26> b
$R0: Board = {
  board = 8 values {
    [0] = 8 values {
      [0] = nil
      [1] = nil
      [2] = nil
      [3] = nil
      [4] = Some
      [5] = nil
      [6] = nil
      [7] = nil
    } ...