A couple of different approaches for Routers on iOS. (by Alexandros, Kamil, Jader & Giuseppe)

Router+protocol.swift

struct NavigatorTypeV2 {}
struct Device {}

protocol Router: class {
    var navigator: NavigatorTypeV2 { get }
}

extension Router {
    public var navigator: NavigatorTypeV2 { fatalError("Not implemented. This router uses a legacy navigator or custom navigation.") }
}


protocol OnboardingRouterHandler: class {
    func onDeviceOnboarded(device: Device)
    func onOnboardCancelled()
}

class OnboardingPRouter: Router {
    private unowned let parentRouter: OnboardingRouterHandler

    init(parentRouter: OnboardingRouterHandler) {
        self.parentRouter = parentRouter
    }

    func start() {
        // ...
    }

    func cancel() {
        parentRouter.onOnboardCancelled()
    }

    func onLastStep(with device: Device) {
        parentRouter.onDeviceOnboarded(device: device)
    }
}

protocol TutorialRouterHandler: class {
    func onTutorialCompleted()
    func onTutorialCancelled()
}

class TutorialRouter: Router {
    private unowned let parentRouter: TutorialRouterHandler

    init(parentRouter: TutorialRouterHandler) {
        self.parentRouter = parentRouter
    }

    func start() {
        // ...
    }

    func onLastStep() {
        parentRouter.onTutorialCompleted()
    }

    func onExit() {
        parentRouter.onTutorialCancelled()
    }
}

class DashboardRouter: Router {
    func start() {
        let onboardingRouter = OnboardingPRouter(parentRouter: self)
        onboardingRouter.start()
    }
}

// MARK: Tutorial routing
extension DashboardRouter: TutorialRouterHandler {
    func onTutorialCompleted() {
        print("User completed tutorial")
    }

    func onTutorialCancelled() {
        print("User Cancelled tutorial")
    }
}

// MARK: Onboarding routing
extension DashboardRouter: OnboardingRouterHandler {
    func onDeviceOnboarded(device: Device) {
        print("The device onboarded is \(device)")
        let tutorialRouter = TutorialRouter(parentRouter: self)
        tutorialRouter.start()
    }

    func onOnboardCancelled() {
        print("User Cancelled Onboarding")
    }
}

Router+simpleResult.swift

struct NavigatorTypeV2 {}
struct Device {}

protocol Router: class {
    var navigator: NavigatorTypeV2 { get }
    func childDidFinish<T>(result: T)
}

extension Router {
    public var navigator: NavigatorTypeV2 { fatalError("Not implemented. This router uses a legacy navigator or custom navigation.") }
    func childDidFinish<T>(result: T) { fatalError("Not Implemented but used") }
}

class TutorialRouter: Router {
    private unowned let parentRouter: Router
    private let device: Device

    enum Result {
        case cancelled
        case completed
    }

    init(parentRouter: Router, device: Device) {
        self.parentRouter = parentRouter
        self.device = device
    }

    func start() {
        // ...
    }

    func onLastStep() {
        parentRouter.childDidFinish(result: Result.cancelled)
    }

    func onExit() {
        parentRouter.childDidFinish(result: Result.completed)
    }
}

class OnboardingRouter: Router {
    private unowned let parentRouter: Router

    enum Result {
        case cancelled
        case deviceOnboarded(Device)
    }

    init(parentRouter: Router) {
        self.parentRouter = parentRouter
    }

    func start() {
        // ...
    }

    func cancel() {
        parentRouter.childDidFinish(result: Result.cancelled)
    }

    func onLastStep(with device: Device) {
        parentRouter.childDidFinish(result: Result.deviceOnboarded(device))
    }
}

class DashboardRouter: Router {
    func start() {
        let onboardingRouter = OnboardingRouter(parentRouter: self)
        onboardingRouter.start()
    }

    func childDidFinish<T>(result: T) {
        switch result {
        case let onboarding as OnboardingRouter.Result:
            handle(result: onboarding)
        case let tutorial as TutorialRouter.Result:
            handle(result: tutorial)
        default:
            fatalError("Missing handling for this child")
        }
    }

    private func handle(result: OnboardingRouter.Result) {
        switch result {
        case .deviceOnboarded(let device):
            let tutorialRouter = TutorialRouter(parentRouter: self, device: device)
            tutorialRouter.start()
        case .cancelled:
            print("Nothing to do here/dismiss")
        }
    }

    private func handle(result: TutorialRouter.Result) {
        switch result {
        case .completed:
            print("Nothing to do here/dismiss")
        case .cancelled:
            print("Nothing to do here/dismiss")
        }
    }
}