Keep var with clj-reload

Christoph Frick - ofnir.net — Wed, 22 Apr 2026 22:00:00 GMT

When writing ring servers it's common pass a var down as handler while developing to make the code reload-able, e.g. #'handler. But when using clj-reload the whole name-space is "replaced" (as in: a new name-space is created, and the old one will GC eventually).

So the handler var the server holds is still fine, but it is the old version. While clj-reload suggests some ways to handle this situation, I wondered how to re-resolve a var, but found no build-in way. So the following function makes sure to resolve the current "version" of the given var:

(defn re-ressolving-var
  [v]
  {:pre [(var? v)]}
  (let [{vns :ns vname :name} (meta v)]
    (ns-resolve (create-ns (.getName vns)) vname)))

And with reitit:

(let [dev-mode? (get opts :dev-mode false)
      rh (if dev-mode?
           (reitit.ring/reloading-ring-handler #(re-ressolving-var handler))
           (handler))]
  (jetty/run-jetty rh opts))))

Christoph Frick - ofnir.net - Open Source Consultant, Software Developer and System Administrator (Posts about clj-reload)

Keep var with clj-reload