Clojurians Log v2

Cheeky proof of concept:

(def nothing (Object.))

(deftype SameContainer [^:volatile-mutable capture]
  clojure.lang.IPersistentCollection
  (equiv [_ other]
    (if (identical? capture nothing)
      (do (set! capture other)
          true)
      (identical? capture other))))

(defn same [] (->SameContainer nothing))

(let [x "some object"
      y "other object"
      data {:a x, :b y, :c [x y x]}

      s1 (same)
      s2 (same)]
 (is (match? {:a s1, :b s2, :c [s1 s2 s1]}
             data)))