LKLabelLayerActions.swift

@objc @NSManaged open dynamic var attributedText : NSAttributedString?

open override func action(forKey event: String) -> CAAction? {
    if event == keyPath(\LKLabelLayer.attributedText) {
        /// Create and return our text interpolating `CAAction` instance here
    }
    return super.action(forKey:event)
}

open override class func needsDisplay(forKey key: String) -> Bool {
    var result = super.needsDisplay(forKey: key)
    result = result || key == keyPath(\LKLabelLayer.attributedText)
    return result
}

func keyPath<Root, Key>(_ keyPath: KeyPath<Root, Key>)->String {
    return NSExpression(forKeyPath: keyPath).keyPath
}