oop-with-inheritance.clj

(ns oop-with-inheritance)

(defn start [arg]
  (println "starting: " arg))

(defn stop [sys]
  (println "stopping:" sys))

(defn server-system-local [& args]
  (apply println "making server system:" args)
  {:hello "world!"})

(defn make-system []
  (let [state (atom nil)]
    (fn [msg & args]
      (case msg
        :start (reset! state (start (apply server-system-local args)))
        :stop (do (stop @state)
                  (reset! state nil))))))

(defn make-derived-system []
  (let [subclass-state (atom {:count 0})
        parent (make-system)]
    (fn [msg & args]
      (case msg
        :inc (:count (swap! subclass-state update-in [:count] inc))
        :dec (:count (swap! subclass-state update-in [:count] dec))
        :stop (do (println "stopping derived system")
                  (parent :stop))
        (apply parent msg args)))))