leveraging call-site caching for getter access

message-map.clj

(defn message-map [msg1]
  (reify
    clojure.lang.IDeref
    (deref [] msg1)
    clojure.lang.IKeywordLookup 
    (getLookupThunk [k]
      (let [getter (->> (name k)
                        (replace-by #"(?:^|-)(.)" #(.toUpperCase (nth % 1)))
                        (str "get")
                        symbol)
            msgmap (gensym)
            msg-hinted (with-meta `(deref ~msgmap)
                                   {:tag (symbol (.getName (class msg1)))})]
        (prn :did k)
        (eval `(reify clojure.lang.ILookupThunk
                      (get [~msgmap] (. ~msg-hinted ~getter))))))))

(def msg1 (-> (make-message-builder) (.setId 3) .build))

(def msg2 (-> (make-message-builder) (.setId 6) .build))

(defn test-get-id [m] (:id (message-map m)))

(test-get-id msg1)
; :did :id
;=> 3

(test-get-id msg1)
;=> 3

(test-get-id msg2)
;=> 6

(test-get-id msg2)
;=> 6