是否在Clojure中订购地图？ [英] Are maps in Clojure ordered?

问题描述

我来自Python，默认情况下，地图（即字典）不排序。开始学习Clojure时，我遇到了这个问题：

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

在我看来，要使这种破坏有效，必须依靠地图排序（当然要记住顺序）。

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?

推荐答案

Clojure映射没有排序，尽管存在诸如排序的问题-地图。由于使用键访问值，因此获得一致的顺序。看看更改键名时会发生什么...

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

我有一个类似的问题，具有与您的问题相关的可接受的答案。

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

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