demonstrating structural sharing in clojure.lang.PersistentVector instances

pv-structure-sharing.clj

;; demonstrating structural sharing
;; in clojure.lang.PersistentVector
;; instances

(let [v1 (vec (range 100))
      v2 (conj v1 :foo)
      v3 (conj v1 :bar)
      v4 (conj (vec (range 100)) :quux)
      PV-root (doto (.getDeclaredField clojure.lang.PersistentVector "root")
                (.setAccessible true))
      v2-root (.get PV-root v2)
      v3-root (.get PV-root v3)
      v4-root (.get PV-root v4)]
  {:v2-and-v3 (identical? v2-root v3-root)
   :v2-and-v4 (identical? v2-root v4-root)})

;; evaluates to
(comment {:v2-and-v3 true, :v2-and-v4 false})