 public extension NSString {
   
   override class func initialize() {
+    guard self == NSString.self else { return }
     let selector: Selector = "sizeWithAttributes:"
     let origIMP = class_getMethodImplementation(self, selector)
     typealias IMPType = @convention(c) (NSString, Selector, AnyObject) -> CGSize

public extension UIMenuController {
  
  override class func initialize() {
    if true {
      let selector: Selector = "setMenuItems:"
      let origIMP = class_getMethodImplementation(self, selector)

public extension UILabel {
  
  override class func initialize() {
    guard self == UILabel.self else { return }
    let selector: Selector = "drawTextInRect:"
    let origIMP = class_getMethodImplementation(self, selector)
    typealias IMPType = @convention(c) (UILabel, Selector, CGRect) -> ()
