Model navigation with value types

navigation.swift

enum Navigation {
    case section(Section)
    case push(Screen)
    case modal(
        Screen,
        UIModalPresentationStyle = .fullScreen,
        completion: (() -> Void)? = nil
    )
}

enum Section {
    case home
    case messages
    case notifications
    case profile
}

struct Screen {
    let viewController: () -> UIViewController
}