gistfile1.txt

// MARK: - UIView Extension for Dance

@available(iOS 10.0, *)
extension UIView {
    
    fileprivate struct DanceAssociatedKey {
        static var dance = "dance_key"
    }
    
    public var dance: Dance {
        get {
            if let danceInstance = objc_getAssociatedObject(self, &DanceAssociatedKey.dance) as? Dance {
                return danceInstance
            } else {
                let newDanceInstance = Dance(dancingView: self)
                objc_setAssociatedObject(self, &DanceAssociatedKey.dance, newDanceInstance, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
                return newDanceInstance
            }
        }
    }
    
}