迭代并打印groovy封闭的内容 [英] Iterate and print content of groovy closures

问题描述

在一个循环中，我创建了4个闭包并将它们添加到列表中：

In a loop I create 4 closures and add them to a list:

closureList = []
for (int i=0; i<4; i++) {
    def cl = {
        def A=i;
    }
    closureList.add(cl)
}
closureList.each() {print  it.call()println "";};

这将产生以下输出：

4
4
4
4

但是我本来希望是0、1、2、3。为什么4个闭包的A值相同？

But I would have expected 0,1,2,3 instead. Why does the 4 closures have the same value for A?

推荐答案

是的，这吸引了人们，自由变量 i 绑定到for循环中的最后一个值，而不是创建闭包时的值。

Yeah, this catches people out, the free variable i is getting bound to the last value in the for loop, not the value at the time the closure was created.

您可以将循环更改为基于闭合的调用：

You can either, change the loop into a closure based call:

closureList = (0..<4).collect { i ->
    { ->
        def a = i
    }
}
closureList.each { println  it() }

或创建一个额外的变量，每次循环时都会重新设置该变量，并使用该变量：

Or create an extra variable that gets re-set every time round the loop, and use that:

closureList = []

for( i in (0..<4) ) {
    int j = i
    closureList << { ->
        def a = j
    }
}
closureList.each { println  it() }

在这两种变体中，每次关闭循环都会重新创建由闭包关闭的变量，因此您可以获得期望的结果

In both of these variants the variable closed by the closure is created afresh each time round the loop, so you get the result you'd expect

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