Function app_window 

pub fn app_window<App: Application>(
    settings: impl Fn(&mut App) -> Settings + Send + Sync + 'static,
    view: Option<Box<dyn for<'a> Fn(&'a App) -> Element<'a, Action<App::Message>> + Send + Sync + 'static>>,
) -> (Id, Action)

Available on crate feature wayland and Linux and crate feature winit only.