带有休息参数的匿名函数抛出NullPointerException [英] Anonymous function with rest parameter throwing NullPointerException

问题描述

这是函数

(#(
   (println (str "first: " %1))
   (println (str "second: " %2))
   (println (str "rest: " (clojure.string/join ", " %&))))
 "f" "s" "x" "y" "z")

在苹果酒中运行时我得到了预期的结果，但是最后我看到我也得到了NullPointerException。

When running this in cider I get the desired result but at the end I see that I am also getting a NullPointerException.

这种形式的匿名函数似乎与

It seems that this form of anonymous function has some issues with destructuring.

因为，当我尝试以下形式的匿名函数时，它起作用。

Because, when I try the following form of anonymous function, it works.

((fn [f s & rest]
    (println (str "first: " f))
    (println (str "second: " s))
    (println (str (clojure.string/join ", " rest))))
   "f" "s" "x" "y" "z")

有人可以解释为什么会这样吗？

Can someone explain why is this happening ?

推荐答案

您需要做：

(#(do
   (println (str "first: " %1))
   (println (str "second: " %2))
   (println (str "rest: " (clojure.string/join ", " %&))))
 "f" "s" "x" "y" "z")

没有 do ，您正在尝试调用第一个 println 的结果，（即在列表的其余元素上 nil ）。 fn 具有隐式 do 。

Without the do, you're trying to invoke the result of the first println, (i.e. nil) on the remaining elements of the list. fn has an implicit do.

情况下，比较（（println））和（do（println））

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