generate_unique_id.clj

(let [a (atom 1)]
  (defn generate-unique-id
    "Returns the next value of a thread-safe incrementing variable."
    []
    (swap!
      a
      #(inc %))))

;; if we use (def) instead of (defn), we can move the atom variable inside the
;; (def) form. We just have to make sure that the atom is only created once, at
;; the beginning, and not every time the function is called.

(def generate-unique-id
  (let [a (atom 1)]
    (fn [] (swap! a #(inc %)))))

;; #(inc %) is the same as inc itself

(def generate-unique-id
  (let [a (atom 1)] (fn [] (swap! a inc))))

;; passing the atom to (partial), which will curry the swap! function, will work too

(def generate-unique-id
  (partial swap! (atom 1) inc))