;; Proxy folds into a delay: the real subject is built at the first deref
;; and never before, so cheap questions cost nothing

;; RealSubject — expensive to make
(defn image [file-name]
  (println "loading" file-name)
  {:file-name file-name
   :draw #(println "draw" file-name)})       ; Request()

;; Proxy — holds the cheap part and a promise of the real one
(defn image-proxy [file-name]
  {:file-name file-name
   :image (delay (image file-name))})

;; Client
(def p (image-proxy "1.png"))
(println (:file-name p))      ; answered without creating the RealSubject
((:draw @(:image p)))         ; now the RealSubject is created
;; 1.png
;; loading 1.png
;; draw 1.png