I decided against using a trait and a derive macro because I wanted to avoid running into Rust's orphan rule. We have a crate called routecore where most of our types are declared and then a separate crate called Rotonda which uses those types and uses Roto. I wanted Rotonda to be able to register routecore types.

That's also the downside of the current reflection crates; they require each type to have a derive macro.