ios - How to resolve this error? - Class 'ViewController' has no initializers -

i have created uilabel programmatically in swift gives me following error :

class 'viewcontroller' has no initializers

code :

class viewcontroller: uiviewcontroller {      let lbl_lastname: uilabel!      override func viewdidload() {         super.viewdidload()         lbl_lastname.frame = cgrectmake(10, 230, 300, 21)         self.view.addsubview(lbl_lastname)        } } 

change let lbl_lastname: uilabel! var lbl_lastname: uilabel!