There are a few different ways one could achieve this. The first options would be to generate a struct: struct RouteUser { route: &'static str,

There are a few different ways one could achieve this. The first options would be to generate a struct: struct RouteUser { route: &'static str, f: fn(_: &mut Request) -> PencilResult } Then given #[route("/user")] fn user(_: &mut Request) -> PencilResult {} You would hijack the `user` function to return an instance of the struct. fn user() -> RouteUser { // The actual function the user wrote: fn user(_: &mut Request) -> PencilResult { // ... } RouteUser { // Generated from the annotation argument route: "/user", f: user } } There is a difference between item decorators (`#[foobar]`) and regular procedural macros and I'm not completely sure if you could in-fact significantly change the given function. I haven't touched procedural macros in a while. To use the above route, you would simply have a `Route` trait perhaps. trait Route {} And implement it for each generated struct: impl Route for RouteUser {} Then you could use the route as app.route(user()); Which could be defined as fn route<R>(r: R) where R: Route { // ... }