Overriding method with selector ‘touchesBegan:withEvent:’ has incompatible type ‘(NSSet, UIEvent) -> ()’

Swift 1.2 (Xcode 6.3) introduced a native Set type that bridges
with NSSet. This is mentioned in the Swift blog and in the
Xcode 6.3 release notes, but apparently not yet added to the official documentation (update: As Ahmad Ghadiri noted, it is documented now).

The UIResponder method is now declared as

func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent)

and you can override it like this:

override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
    if let touch = touches.first as? UITouch {
        // ...
    }
    super.touchesBegan(touches , withEvent:event)
}

Update for Swift 2 (Xcode 7): (Compare Override func error in Swift 2)

override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
    if let touch = touches.first {
        // ...
    }
    super.touchesBegan(touches, withEvent:event)
}

Update for Swift 3:

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    if let touch = touches.first {
        // ...
    }
    super.touchesBegan(touches, with: event)
}