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