副作用最优化 [英] Side effect optimized out

问题描述

我是clojure的新手，有时会遇到问题。

I am new to clojure and at some moment I faced with the problem.

我的程序中有以下代码：

I have such code in my program:

(let [ ... ]
    (map (fn [[v f]] (do-side-effect v f)) {:v1 f1, :v2 f2})
    (do-the-job ...))

此 do-副作用-code>可以是例如 intern等另一个副作用函数的 println 。问题是不会发生副作用。

This do-side-effect can be, for example, println of another side effect function like intern. The problem is that side effect doesn't happen.

但是如果我将行更改为

(println (map #(fn [[v f]] (do-side-effect v f)) {:v1 f1, :v2 f2}))

然后一切正常。
所以我最后想到的是clojure
只是优化了 map ，因为
认为结果没有用，因为我不要使用它。

Then everything is ok. So the last idea i came to is that clojure just optimize out the map because it think that it's result is useless because I don't use it.

万一这种情况真的发生了，我该如何证明这种形式的
会产生副作用以防止编译器对其进行优化？

In case if this actually happens, how can I show clojure that this form can have side effects to prevent compiler from optimizing it out?

如果它是一个错误，如何找到错误所在？

In case if it's a bug, how can I find where the bug is?

推荐答案

map 很懒。它并不是要直接用于副作用，它只会在消耗它们时产生值。

map is lazy. It is not meant to be used directly for side effects, and it only produces values when they are consumed.

您可以使用 dorun 强制实现这些值，即使您不使用它们，也可以使用 doseq 代替map doseq 用于产生副作用，与map不会花费时间来构造您永远不会访问的对象。

You can use dorun to force the values to be realized, even if you are not consuming them, or use doseq instead of map, doseq is intended to be used for side effects, and unlike map won't spend time constructing objects you won't ever access.

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