Function actix_service::factory_fn

pub fn factory_fn<F, Cfg, Srv, Fut, Err>(
    f: F
) -> FnServiceNoConfig<F, Cfg, Srv, Fut, Err> where
    Srv: Service,
    F: Fn() -> Fut,
    Fut: Future<Output = Result<Srv, Err>>, 

Create ServiceFactory for function that can produce services