I agree that allowing implementing long polling with crow is important, just I didn't know a good way to do that. Your suggestion is big help.

I think supporting both way is better if there is a enough explanation. I don't want to drop a simpler way to do the same job.

  CROW_ROUTE(app, "/about")
    ([](){
        return "About Crow example";
    });

  CROW_ROUTE(app, "/about")
    ([](Response res){
        res.send("About Crow example");
    });