Is there a typesafe way to use selectors in Swift?

Question

For the most part, Swift is a huge improvement over Objective-C in terms of type safety. One glaring exception is selectors. In Objective-C, using the expression @selector(notARealSelector:) will give a compiler warning. The Swift equivalent, Selector("notARealSelector:") will always compile but will fail at runtime.

Is there a typesafe way to use selectors in Swift, so I can work with Objective-C APIs that require them?

I have a lot of NSNotification observers in my app and would like to have some kind of compile-time checking that I'm not making typos in my selectors.

Edit: The specific use case is NSNotificationCenter.addObserver.

Answer 1

Typesafe selectors were just released in Xcode 7.3 beta 4:

let sel = #selector(insertSubview(_:aboveSubview:)) // sel has type 

Selector is now a first class citizen and comes with some nice Swift compiler warnings. If needed you can still pass in a string:

let sel = Selector("propertyName") 

See a much more complete answer here: @selector() in Swift?

Xcode Release Notes: http://adcdownload.apple.com/Developer_Tools/Xcode_7.3_beta_4/Xcode_7.3_beta_4_Release_Notes.pdf

Answer 2

Use the Swift notion of optionals as:

if let result = object.notARealSelector?(/* args */) {    // Use Result } 

where the ? used following notARealSelector with return false to if when there is no such method defined on the type of object.

There is a caveat for optional protocol requirements:

Optional protocol requirements can only be specified if your protocol is marked with the @objc attribute. Even if you are not interoperating with Objective-C, you need to mark your protocols with the @objc attribute if you want to specify optional requirements.

But since your are asking about optional methods in the first place, you must be talking about this in the Objective-C context.