Swift通用2d阵列

Question

I'm looking to do something relatively simple. I want a 2 dimension array of a generic type. From what I understand, I should use two sets of square braces surrounding the base type, and I can use the simplified loop expression to init the values. I have the below code, but I'm receiving an error, cannot be constructed because it has no accessible initializes . Below is the code I'm using. Thank you in advance for any help.

array = [[Element]](count: 3, repeatedValue: Element(count: 2, repeatedValue: nil))

edit : I wanted to provide the full source of the code I'm working with

struct Array2D<Element> {
    let columns: Int
    let rows: Int
    private var array: Array<Element?>

    init(columns: Int, rows: Int) {
        self.columns = columns
        self.rows = rows
        array = [[Element]](count: 3, repeatedValue: Element(count: 2, repeatedValue: nil))
    }

    subscript(column: Int, row: Int) -> Element? {
        get {
            return array[row*columns + column]
        }
        set {
            array[row*columns + column] = newValue
        }
    }
}

Answer 1

The

private var array: Array<Element?>

property in Array2D is a normal ("one-dimensional") array used for the storage of the rows * columns elements. It must be initialized with:

array = [Element?](count: rows * columns, repeatedValue: nil)

or just (because the type is known):

array = Array(count: rows * columns, repeatedValue: nil)

Answer 2

Swift doesn't know Element has an intializer for the Element type.

Here's how you can do it with a helper class:

class TwoDArray<T> {
    static func create(initialValue: T, rows: Int, cols: Int) -> [[T]] {
        let tmp = [T](count: cols, repeatedValue: initialValue)
        return [[T]](count: rows, repeatedValue: tmp)
    }
}

let result = TwoDArray.create(42, rows: 3, cols: 2)

If you want to initiate the array with nil , you have to supply an optional type:

let result = TwoDArray<Int?>.create(nil, rows: 3, cols: 2)