为什么我不能修改一个foreach循环变量？ [英] Why can't I modify the loop variable in a foreach?

问题描述

为什么一个的foreach 循环只读循环？是什么原因，有这个？

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

推荐答案

我不知道用只读循环你的意思是什么，但我猜你想知道为什么这个不能编译：

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;
}

以上code将使以下编译错误：

The above code will give the following compile error:

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

这是为什么不允许？试图分配给它可能不会做你想要的 - 它不会修改原始集合的内容。这是因为，变量x是不要在列表中的元素的引用 - 它是一个拷贝。为了避免人车写作code，编译器不允许这样。

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.

这篇关于为什么我不能修改一个foreach循环变量？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！