gistfile1.txt

(ns destructors)

(defprotocol Disposable
  (dispose [obj] "Dispose obj"))

(declare *registered-objects*)

(defn to-dispose
  [obj]
  (swap! *registered-objects* conj obj)
  obj)

(defn cleanup
  []
  (doseq [obj @*registered-objects*]
    (dispose obj)))

(defmacro with-destructors
  [& body]
  `(binding [*registered-objects* (atom nil)]
     (try
       ~@body
       (finally (cleanup)))))

(extend-type java.io.Closeable
  Disposable
  (dispose [obj]
     (.close obj)))

;;; Example usage

(defn write-demo-file
  [string]
  (with-destructors
    (let [fw (to-dispose (java.io.FileWriter. "/tmp/test"))]
      (.write fw string 0 (count string)))))

(defmacro my-with-open
  [bindings & body]
  (let [new-bindings (map #(if %1 %2 `(to-dispose ~%2))
			  (cycle [true false])
			  bindings)]
    `(with-destructors
       (let [~@new-bindings]
	 ~@body))))