func scrollViewWillEndDragging (scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        
        // how to get value from targetContentOffset:
        let y = targetContentOffset.memory.y
        
        // how to set value to targetContentOffset:
        targetContentOffset.memory.y = 0 //i.e. amount * value
    }