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) {

        }
    }
}

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