Error on line 23, pointing to the size() call: Cannot convert type 'Int' to expected argument type 'Int'

Matrix.swift

protocol Matrix {
    typealias ElementType

    static func dimensions() -> (rows: Int, cols: Int)
    static func size() -> Int

    init()

    subscript(row: Int, col: Int) -> ElementType { get set }
}


struct Matrix4<T: FloatingPointType> : Matrix {
    static func dimensions() -> (rows: Int, cols: Int) {
        return (4, 4)
    }

    static func size() -> Int {
        let dimensions = Matrix4.dimensions()
        return dimensions.rows * dimensions.cols
    }

    private var data: [T] = [T](count: Matrix4.size(), repeatedValue: T(0))

    init() {
        data = [T](count: Matrix4.size(), repeatedValue: T(0))
    }

    subscript(row: Int, col: Int) -> T {
        get {

        }
        set(value) {

        }
    }
}

Often, changing the definition to an equivalent one yields a different error which sheds more light on the problem (or at least narrows down which subexpression is responsible). For example, changing the definition to:

private var data: [T] = { (value: T) in
    [T](count: Matrix4.size(), repeatedValue: value)
}(T(0))

yields:

boom.swift:26:3: error: cannot invoke closure of type '(T) -> [T]' with an argument list of type '(T)'
}(T(0))
~^

With some further experimentation, it looks like Swift doesn’t like expressions involving T at this scope; by contrast, the init you wrote seems fine. Seems radar-worthy.

This turned out to be a name lookup bug. You can work around it in Swift 2 by using "Matrix4.size()" to specifically provide the type bound, but it is now fixed for Swift 3 as of Swift.org commit b3ac017.

That was supposed to be Matrix4 < T > .size()