Is that a bug in Swift Compiler?

Question

I write a protocol (in Xcode playground),and want it be conform by specified class , eg: Root.

Because I used Swift 4.1 , So there are new syntax for this :

protocol Delegate where Self:Root{
 var titleImage:UIImage? {get}
}

(PS:If you want to know more about this , please follow the link : How to make Swift protocol conformed by a specific kind of Class?)

And I also write class Root and Foo :

class Root:Delegate{
 var titleImage:UIImage?
 func willDo(){
 let foo = Foo()
 foo.delegate = self
 foo.invoke()
 }
}
class Foo{
 var delegate:Delegate!
 func invoke(){
 if let image = delegate.titleImage{
 print("have a image [\(image)")
 }else{
 print("not have a image")
 }
 }
}

Problem is that when I call :

let r = Root()
r.willDo()

Here are runtime error :

enter image description here

But when I changed Delegate code to this :

protocol Delegate{
 var titleImage:UIImage? {get}
}

That's all right!!! But it can't limited Delegate to be conform by class Root anymore!

Could anyone can tell me Why is it? Why when add " Self:Root " to Delegate will trigger a BAD_ACCESS Runtime error???

Is this a Bug in Swift or I misunderstand something???

Thanks a lot ;)

• Hamish: AFAIK being able to use class constraints in protocol where clauses isn't something that's fully supported currently – that's tracked by SR-6001. The specific runtime crash you're getting looks like SR-6816.
• hopy: @NaderBesada Is your Swift 4.1 in Version 9.3 (9E145) ??? Ary you mean my Xcode Version is too old???
• hopy: So it's seem be a Bug??? @Hamish
• hopy: Restart Xcode or test in real project (not in playground) are all not working... But thank you anyway ;) @NaderBesada

Answer 1

Add @objc when declaring your protocol

@objc protocol Delegate where Self: Root{
 var titleImage: UIImage? {get}
}

This is a current bug in swift so wrapping it in @objc should work