=和==在Clojure [英] = and == in Clojure

问题描述

在REPL上，如果我定义

On REPL, if I define

(def fits (map vector (take 10 (iterate inc 0))))

然后调用

(== [2] (nth fits 2))

但

(= [2] (nth fits 2))

返回true。

这个预期？我试过（类[2]）和（类（nth适合2），并且都返回持久向量。

Is this expected ? I tried (class [2]) and (class (nth fits 2) and both return Persistent Vector.

推荐答案

== 用于比较数字。如果其中任何一个参数不是数字，它总是返回false：

== is for comparing numbers. If either of its arguments is not a number, it will always return false:

(== :a :a)
; => false

正如你可以看到，在REPL处有（clojure.contrib.repl-utils / source ==）（ repl-utils 'd，当然）， == equiv 的方法clojure.lang.Numbers 。 clojure / lang / Numbers.java （从GitHub的最新或接近最新的提交）：

As you can see by saying (clojure.contrib.repl-utils/source ==) at the REPL (with repl-utils require'd, of course), == calls the equiv method of clojure.lang.Numbers. The relevant bit of clojure/lang/Numbers.java (from the latest or close-to-latest commit on GitHub):

static public boolean equiv(Object x, Object y){
    return y instanceof Number && x instanceof Number
           && equiv((Number) x, (Number) y);
}

使用 = 可以不等于数字的平等比较。当你事实上处理数字时， == 应该有点快。

Use = for equality comparisons of things which may not be numbers. When you are in fact dealing with numbers, == ought to be somewhat faster.

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