在协议扩展中将nil传递给具有可选的一般约束参数的函数

Question

I have a situation where I declare two functions in a protocol, one of them takes an optional generically constrained parameter, the other function takes no parameters, but needs to be implemented in an extension as a default function where it calls the one with a parameter and passes nil . However I get this error:

Argument passed to call that takes no arguments

My code:

public protocol MenuAccessible {
    var menuEntryViewController: UIViewController { get }
}

public protocol MenuTabBarControllerProtocol {
    func reloadTabs<T>(from uiProvider: T?) where T: MenuAccessible
    func reloadTabs()
}

public extension MenuTabBarControllerProtocol {
    func reloadTabs() {
        reloadTabs(from: nil) // error here, can't infer type
    }
}

Obviously the compiler is not able to infer the type. If I for example pass a nil ( Optional ) of the required type, then the compiler is happy. For example:

struct MenuAccessibleObject: MenuAccessible {
    var menuEntryViewController: UIViewController { return UIViewController() }
}

public extension MenuTabBarControllerProtocol {
    func reloadTabs() {
        let menuAccessible: MenuAccessibleObject? = nil
        reloadTabs(from: menuAccessible) // passes nil, but compiler is happpy
    }
}

Is there a way to pass nil in my default function implementation and not have to create that dummy object?

Answer 1

I don't understand why you are Using Generic T there if you are defining type is MenuAccessible

Following is simply compiler without any issue

public protocol MenuAccessible {
    var menuEntryViewController: UIViewController { get }
}

public protocol MenuTabBarControllerProtocol {
    func reloadTabs(from uiProvider: MenuAccessible?)
    func reloadTabs()

}

public extension MenuTabBarControllerProtocol {
    func reloadTabs() {
        reloadTabs(from: nil)
    }

}

public extension MenuTabBarControllerProtocol {
    func reloadTabs(from uiProvider: MenuAccessible?)  {
        fatalError() // implement me
    }
}

EDIT

I don't know this will work for you or not but try this

public protocol MenuAccessible {
    var menuEntryViewController: UIViewController { get }
}


public class UIProvider:NSObject {

}

public protocol MenuTabBarControllerProtocol {

    func reloadAllTheItems<T>(from uiProvider: T?) where T: UIProvider, T: MenuAccessible
    func reloadTabs()
}

public extension MenuTabBarControllerProtocol {

    func reloadTabs() {
        self.reloadAllTheItems(from: Temp())
    }

    func reloadAllTheItems (provider:(UIProvider &  MenuAccessible)) {

    }


}

class Temp: (UIProvider &  MenuAccessible) {
    var menuEntryViewController: UIViewController {
        return UIViewController()
    }

}