non-nominal type X does not support explicit initialization

Question

I'm trying to understand what I'm doing wrong with generics in swift.

I created this sample playground

import UIKit

public protocol MainControllerToModelInterface : class {
    func addGoal()
    init()
}

public protocol MainViewControllerInterface : class {
    associatedtype MODELVIEW
    var modelView: MODELVIEW? {get set}

    init(modelView: MODELVIEW)
}

public class MainViewController<M> : UIViewController, MainViewControllerInterface where M : MainControllerToModelInterface {
    public weak var modelView: M?

    required public init(modelView: M) {
        self.modelView = modelView
        super.init(nibName: String(describing: MainViewController.self), bundle: Bundle.main)
    }

    required public init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

public class Other<C, M> : NSObject where C : MainViewControllerInterface, C : UIViewController, M : MainControllerToModelInterface, C.MODELVIEW == M {
    var c : C?

    override init() {
        let m = M()
        self.c = C(modelView: m)
        super.init()
    }
}

the line self.c = C(modelView: m) gives me this error non-nominal type 'C' does not support explicit initialization

From this other stack overflow question I see that this error in older Xcode versions means

cannot invoke initializer for type '%type' with an argument list of type '...' expected an argument list of type '...'

But in the playground above what is the compiler missing?

I'm on swift4/xcode9.

Update

After following the suggestion Use C.init(modelView: m) rather than C(modelView: m) the error changes in:

No 'C.Type.init' candidates produce the expected contextual result type '_?'

Than @vini-app suggested to remove the UIViewController to make it works. By I still don't understand why the compiler is not happy when UIViewController is there. Is it not enough to know that C has that valid init method?

score 51 · Accepted Answer · answered Sep 27 '17 at 23:27

51

You just need to use init explicitly whenever you're initializing a generic parameter rather than a "real" type:

self.c = C.init(modelView: m)

answered Sep 27 '17 at 23:27

andyvn22

14,696
1
52
74

Thanks, than I get `No 'C.Type.init' candidates produce the expected contextual result type '_?'` – Luca Bartoletti Sep 27 '17 at 23:31
it's not working Swift 4.1. I have to remove UIViewController constrained. but I need this constraint. any idea how to fix? – Hashem Aboonajmi May 26 '18 at 19:24
add the required statement before your init definition and this works – Igor Muzyka Jul 30 '18 at 20:57

score 3 · Answer 2 · answered Sep 27 '17 at 23:27

3

Use C.init(modelView: m) rather than C(modelView: m). That should fix it.

answered Sep 27 '17 at 23:27

rounak

9,217
3
42
59

Thanks, than I get `No 'C.Type.init' candidates produce the expected contextual result type '_?'` – Luca Bartoletti Sep 27 '17 at 23:31
1

On my main project this actually solves the issue. But giving the check to the other answer because it was first. Thanks again! – Luca Bartoletti Sep 28 '17 at 21:31

score 1 · Answer 3 · answered Sep 28 '17 at 00:31

1

Please check :

In your code you are doing like this C : MainViewControllerInterface, C : UIViewController.

It is treating C as ViewController, then there is no init in ViewController like init(modelView: M) thats why its throwing error

public class Other<C, M> : NSObject where C : MainViewControllerInterface, M : MainControllerToModelInterface, C.MODELVIEW == M {
    var c : C?

    override init() {
        let m = M()
        self.c = C(modelView: m)
        super.init()
    }
}

answered Sep 28 '17 at 00:31

Vini App

7,339
2
26
43

Thanks, but C is `C : MainViewControllerInterface`. That protocol defines the initializer i’m using there. – Luca Bartoletti Sep 28 '17 at 00:35
After deleting ViewController, its working. Please check my code. – Vini App Sep 28 '17 at 00:36
Yes, but still, it's like the thing it's that I need that. you say that `It is treating C as ViewController, then there is no init in ViewController like init(modelView: M) thats why its throwing error` but this doesn't make sense to me. C is also adopting `MainViewControllerInterface`, so why is not enough for the compiler? – Luca Bartoletti Sep 28 '17 at 09:17
Is because UIViewController is a class and not a protocol? – Luca Bartoletti Sep 28 '17 at 09:44

non-nominal type X does not support explicit initialization

3 Answers3

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