Search code examples
pythonclojure

Are maps in Clojure ordered?

I'm coming from Python where maps (i.e. dicts) are not ordered by default. Starting to learn Clojure and I came across this:

(def point {:x 5 :y 7})
=> #'user/point
point
=> {:x 5, :y 7}
(let [{:keys [x y]} point]
  (println "x:" x "y:" y))
x: 5 y: 7

It seems to me that for this destructuring to work one would have to rely on the map being ordered (and of course, remembering the order). Is that true?

Solution

  • Clojure maps are not ordered, although there is a such thing as a sorted-map. You are getting a consistent order because you are using the keys to access the values. See what happens when you change the key names...

    user=> point
{:a 5, :b 7}

user=> (let [{:keys [x y]} point]
  #_=>   (println "x:" x "y:" y))
x: nil y: nil
nil

user=> (let [{:keys [a b]} point]
  #_=>   (println "a:" a "b:" b))
a: 5 b: 7

    I had a similar question that has an accepted answer that is relevant to your question.