为什么我不能在 foreach 中修改循环变量? [英] Why can't I modify the loop variable in a foreach?

问题描述

为什么 foreach 循环是只读循环?造成这种情况的原因是什么?

解决方案

我不确定您所说的只读循环"究竟是什么意思，但我猜您想知道为什么这不能编译:

int[] ints = { 1, 2, 3 };foreach (int x in int){x = 4;}

以上代码会出现如下编译错误:

<前>无法分配给x"，因为它是foreach 迭代变量"

为什么不允许这样做?尝试分配给它可能不会做你想做的 - 它不会修改原始集合的内容.这是因为变量 x 不是对列表中元素的引用——它是一个副本.为了避免人们编写错误代码，编译器不允许这样做.

Why is a foreach loop a read only loop? What reasons are there for this?

解决方案

I'm not sure exactly what you mean by a "readonly loop" but I'm guessing that you want to know why this doesn't compile:

int[] ints = { 1, 2, 3 };
foreach (int x in ints)
{
    x = 4;
}

The above code will give the following compile error:

Cannot assign to 'x' because it is a 'foreach iteration variable'

Why is this disallowed? Trying to assigning to it probably wouldn't do what you want - it wouldn't modify the contents of the original collection. This is because the variable x is not a reference to the elements in the list - it is a copy. To avoid people writing buggy code, the compiler disallows this.

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