import Foundation
import UIKit

extension NSObject {
   final func calculate<T>(_ operation: () -> T) -> T {
      return operation()
   }
}

extension UIButton {
   var calculatedTitle: String {
      return self.calculate { [unowned self] in
         return self.currentTitle!
      }
   }
}

let button = UIButton()
button.setTitle("Hello", for: .normal)

print(button.calculatedTitle)