Functional Button

func_button.swift

typealias UIButtonTargetClosure = (UIButton) -> ()

class ClosureWrapper: NSObject {
  let closure: UIButtonTargetClosure
  init(_ closure: @escaping UIButtonTargetClosure) {
    self.closure = closure
  }
}

extension UIButton {
  
  private struct AssociatedKeys {
    static var targetClosure = "targetClosure"
  }
  
  private var targetClosure: UIButtonTargetClosure? {
    get {
      guard let closureWrapper = objc_getAssociatedObject(self, &AssociatedKeys.targetClosure) as? ClosureWrapper else { return nil }
      return closureWrapper.closure
    }
    set(newValue) {
      guard let newValue = newValue else { return }
      objc_setAssociatedObject(self, &AssociatedKeys.targetClosure, ClosureWrapper(newValue), objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
    }
  }
  
  func addTargetClosure(closure: @escaping UIButtonTargetClosure) {
    targetClosure = closure
    addTarget(self, action: #selector(UIButton.closureAction), for: .touchUpInside)
  }
  
  @objc func closureAction() {
    guard let targetClosure = targetClosure else { return }
    targetClosure(self)
  }
}

https://medium.com/@jackywangdeveloper/swift-the-right-way-to-add-target-in-uibutton-in-using-closures-877557ed9455