这是此模式的Swift版本：

尽管forwardInvocation:已在Swift中禁用，但我们仍然可以使用forwardingTargetForSelector:

class MyScrollView: UIScrollView {

    class _DelegateProxy: NSObject, UIScrollViewDelegate {
        weak var _userDelegate: UIScrollViewDelegate?

        override func respondsToSelector(aSelector: Selector) -> Bool {
            return super.respondsToSelector(aSelector) || _userDelegate?.respondsToSelector(aSelector) == true
        }

        override func forwardingTargetForSelector(aSelector: Selector) -> AnyObject? {
            if _userDelegate?.respondsToSelector(aSelector) == true {
                return _userDelegate
            }
            else {
                return super.forwardingTargetForSelector(aSelector)
            }
        }

        func viewForZoomingInScrollView(scrollView: MyScrollView) -> UIView? {
            return scrollView.viewForZooming()
        }

        // Just a demo. You don't need this.
        func scrollViewDidScroll(scrollView: MyScrollView) {
            scrollView.didScroll()
            _userDelegate?.scrollViewDidScroll?(scrollView)
        }
    }

    private var _delegateProxy =  _DelegateProxy()

    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        super.delegate = _delegateProxy
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        super.delegate = _delegateProxy
    }

    override var delegate:UIScrollViewDelegate? {
        get {
            return _delegateProxy._userDelegate
        }
        set {
            self._delegateProxy._userDelegate = newValue;
            /* It seems, we don't need this anymore.
            super.delegate = nil
            super.delegate = _delegateProxy
            */
        }
    }

    func viewForZooming() -> UIView? {
        println("self viewForZooming")
        return self.subviews.first as? UIView // whatever
    }

    func didScroll() {
        println("self didScroll")
    }
}