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I'm expanding the functionality of this SO answer.

I'm expanding the functionality of this SO answer.

let btn = UIButton()
btn.on(.TouchUpInside) { sender, _ in
    sender.setTitle("Pushed !!", forState: .Normal)
}

Any ideas?

Added: to reply the @nhgrif answer:

Why I did not implement the sender only version like this:

func on<T: UIControl>(events:UIControlEvents, _ callback: T -> Void) -> EventHandlerId {
    assert(self.isKindOfClass(T), "The handler must receive \(NSStringFromClass(self.dynamicType)) or UIControl")
    return self._on(events, EventHandler({ sender, _ in callback(sender as T) }, oneshot: true))
}

That is because of a purely technical problem: It conflict with () -> Void version.

btn.on(.TouchUpInside) { return }                       // OK: () -> Void
btn.on(.TouchUpInside) { (sender: UIButton) in return } // OK: T -> Void
btn.on(.TouchUpInside) { sender in return }             // NG: () -> Void

In the last case, the compiler infers the type of sender as () :(

And why I declared EventHandler as private, that is I don't want users do like this:

let handler = UIControl.EventHandler({ ... }, oneshot: true)

btn.on(.TouchUpInside, handler)
btn.on(.TouchDown, handler)
btn.off(handler)

With my current code, .off() removes the handler from .AllEvents, and from associated objects. There is no way to remove it from specific event. Maybe, if we do want to do that, we can remember the registered events and handle them, but It's too much I think. Moreover, for such use case, we can simply use addTarget() and removeTarget() with custom handler object.

let btn = UIButton()
btn.on(.TouchUpInside) { sender, _ in
    sender.titleLabel.text = "Pushed !!"
}

Any ideas?

let btn = UIButton()
btn.on(.TouchUpInside) { sender, _ in
    sender.titleLabel.text = "Pushed !!"
}

btn.on(.TouchUpInside) { return }                    // OK: () -> Void
btn.on(.TouchUpInside) { sender:UIButton in return } // OK: T -> Void
btn.on(.TouchUpInside) { sender in return }          // NG: () -> Void

let btn = UIButton()
btn.on(.TouchUpInside) { sender, _ in
    sender.setTitle("Pushed !!", forState: .Normal)
}

btn.on(.TouchUpInside) { return }                       // OK: () -> Void
btn.on(.TouchUpInside) { (sender: UIButton) in return } // OK: T -> Void
btn.on(.TouchUpInside) { sender in return }             // NG: () -> Void