Swift extensions to add "center" to CGRect

CGRect+Center.swift

extension CGRect
{
    /** Creates a rectangle with the given center and dimensions
    - parameter center: The center of the new rectangle
    - parameter size: The dimensions of the new rectangle
     */
    init(center: CGPoint, size: CGSize)
    {
        self.init(x: center.x - size.width / 2, y: center.y - size.height / 2, width: size.width, height: size.height)
    }
    
    /** the coordinates of this rectangles center */
    var center: CGPoint
        {
        get { return CGPoint(x: centerX, y: centerY) }
        set { centerX = newValue.x; centerY = newValue.y }
    }
    
    /** the x-coordinate of this rectangles center
    - note: Acts as a settable midX
    - returns: The x-coordinate of the center
     */
    var centerX: CGFloat
        {
        get { return midX }
        set { origin.x = newValue - width * 0.5 }
    }
    
    /** the y-coordinate of this rectangles center
     - note: Acts as a settable midY
     - returns: The y-coordinate of the center
     */
    var centerY: CGFloat
        {
        get { return midY }
        set { origin.y = newValue - height * 0.5 }
    }
    
    // MARK: - "with" convenience functions
    
    /** Same-sized rectangle with a new center
    - parameter center: The new center, ignored if nil
    - returns: A new rectangle with the same size and a new center
     */
    func with(center: CGPoint?) -> CGRect
    {
        return CGRect(center: center ?? self.center, size: size)
    }
    
    /** Same-sized rectangle with a new center-x
    - parameter centerX: The new center-x, ignored if nil
    - returns: A new rectangle with the same size and a new center
     */
    func with(centerX: CGFloat?) -> CGRect
    {
        return CGRect(center: CGPoint(x: centerX ?? self.centerX, y: centerY), size: size)
    }

    /** Same-sized rectangle with a new center-y
    - parameter centerY: The new center-y, ignored if nil
    - returns: A new rectangle with the same size and a new center
     */
    func with(centerY: CGFloat?) -> CGRect
    {
        return CGRect(center: CGPoint(x: centerX, y: centerY ?? self.centerY), size: size)
    }
    
    /** Same-sized rectangle with a new center-x and center-y
    - parameter centerX: The new center-x, ignored if nil
    - parameter centerY: The new center-y, ignored if nil
    - returns: A new rectangle with the same size and a new center
     */
    func with(centerX: CGFloat?, centerY: CGFloat?) -> CGRect
    {
        return CGRect(center: CGPoint(x: centerX ?? self.centerX, y: centerY ?? self.centerY), size: size)
    }
}