Swift Property that conforms to a Protocol and Class

Question

@property (strong, nonatomic) UIViewController<UITableViewDelegate> *thing; 

I want to implement a property like in this Objective-C code in Swift. So here is what I've tried:

class AClass<T: UIViewController where T: UITableViewDelegate>: UIViewController {     var thing: T! } 

This compiles. My problem comes when I add properties from the storyboard. The @IBOutlet tag generates an compiler error.

class AClass<T: UIViewController where T: UITableViewDelegate>: UIViewController {     @IBOutlet weak var anotherThing: UILabel!  // error     var thing: T! } 

The error:

Variable in a generic class cannot be represented in Objective-C 

Am I implementing this right? What can I do to fix or get around this error?

EDIT:

Swift 4 finally has a solution for this problem. See my updated answer.

Answer 1

Update for Swift 4

Swift 4 has added support for representing a type as a class that conforms to a protocol. The syntax is Class & Protocol. Here is some example code using this concept from "What's New in Swift" (session 402 from WWDC 2017):

protocol Shakeable {     func shake() } extension UIButton: Shakeable { /* ... */ } extension UISlider: Shakeable { /* ... */ }  // Example function to generically shake some control elements func shakeEm(controls: [UIControl & Shakeable]) {     for control in controls where control.isEnabled {         control.shake()     } } 

As of Swift 3, this method causes problems because you can't pass in the correct types. If you try to pass in [UIControl], it doesn't have the shake method. If you try to pass in [UIButton], then the code compiles, but you can't pass in any UISliders. If you pass in [Shakeable], then you can't check control.state, because Shakeable doesn't have that. Swift 4 finally addressed the topic.

Old Answer

I am getting around this problem for the time being with the following code:

// This class is used to replace the UIViewController<UITableViewDelegate>  // declaration in Objective-C class ConformingClass: UIViewController, UITableViewDelegate {}  class AClass: UIViewController {     @IBOutlet weak var anotherThing: UILabel!     var thing: ConformingClass! } 

This seems hackish to me. If any of the delegate methods were required, then I would have to implement those methods in ConformingClass (which I do NOT want to do) and override them in a subclass.

I have posted this answer in case anyone else comes across this problem and my solution helps them, but I am not happy with the solution. If anyone posts a better solution, I will accept their answer.