gistfile1.clj

(ns user)

;Version A
(def users 
  {:by-name (ref {})
   :by-id (ref {})
   :next-id (ref 0)})

(defn create-user
  "Creates a user"
  [name]
  (dosync
    (let [new-user {:name name :id @(users :next-id)}]
      (alter (users :next-id) + 1)
      (alter (users :by-name) conj {name new-user})
      (alter (users :by-id) conj {(new-user :id) new-user})
      new-user)))

(def jonas (create-user "Jonas"))



;Version B
(comment
(def users 
  (ref 
    {:by-name {}
     :by-id {}
     :next-id 0 })
  )

(defn create-user
  "Creates a user"
  [name]
  (dosync
    (let [new-user {:name name :id (@users :next-id)}]
      (alter users conj @users {:next-id (+ 1 (@users :next-id))})
      (commute users conj @users {:by-name (conj (@users :by-name) {name new-user})})
      (commute users conj @users {:by-id (conj (@users :by-id) {(new-user :id) new-user})})
      new-user)))


(def jonas (create-user "Jonas"))
)