Swift generics postponed issue

Question

I'm trying to do this but I'm getting some troubles

This is CustomProtocol

protocol CustomProtocol {

}

SubCustomProtocol

protocol SubCustomProtocol: CustomProtocol {

}

SubCustomProtocolImplementation

class SubCustomProtocolImplementation: SubCustomProtocol {

}

This is CustomClass

class CustomClass<P: CustomProtocol> {

    var customProtocol: P?

    func doSomething() {

    } 

}

SubCustomClass

class SubCustomClass<P: SubCustomProtocol>: CustomSubClass {

}

And my BaseViewController

class BaseViewController<P: CustomProtocol, T: CustomClass<P>>: UIViewController {

    var foo: T!

    override func viewDidLoad() {
        super.viewDidLoad()
        foo?.doSomething()
    }
}

My ViewController

class ViewController<P: SubCustomProtocolImplementation, T: SubCustomClass<P>>: BaseViewController<P,T> {

    override func viewDidLoad() {
        super.viewDidLoad()
    }
}

In the line where I call foo?.doSomething() it says that 'T' is not a subtype of 'CustomClass<'P'>' and I don't know what I'm doing wrong

And in the ViewController declaration it says that "BaseViewController requires that T inherit from CustomClass<'P'>"

Hope you can help me!

I'm not getting this error. At least in playground. Are you sure you're providing the full context? — iyuna, Feb 12 '16 at 08:49
It seems, a type parameter cannot be constrained by a generic class. It _can_ be constrained by a class or a protocol. — CouchDeveloper, Feb 12 '16 at 09:18
@CouchDeveloper so basically I can't postpone generics right? — Roberto Frontado, Feb 12 '16 at 09:48
It seems we cannot do this yet. Swift is still not a complete full-fledged language. I would recommend to file a feature request. At least you can work around it, as shown by @lyuna. — CouchDeveloper, Feb 12 '16 at 12:33

score 2 · Answer 1 · answered Feb 12 '16 at 09:05

2

If you want to specify your foo var type as CustomClass<P> you should do as following instead.

class ViewController<P: CustomProtocol>: UIViewController {

    var foo: CustomClass<P>?

    override func viewDidLoad() {
        super.viewDidLoad()
        foo?.doSomething()
    }
}

answered Feb 12 '16 at 09:05

iyuna

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thanks I know, I wasn't explaining it very well, I've edited my question again – Roberto Frontado Feb 12 '16 at 09:17

Swift generics postponed issue

1 Answers1