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");
});