为什么我们不能分配一个 foreach 迭代变量，而我们可以用访问器完全修改它? [英] Why can't we assign a foreach iteration variable, whereas we can completely modify it with an accessor?

问题描述

I was just curious about this: the following code will not compile, because we cannot modify a foreach iteration variable:

        foreach (var item in MyObjectList)
        {
            item = Value;
        }

But the following will compile and run:

        foreach (var item in MyObjectList)
        {
            item.Value = Value;
        }

Why is the first invalid, whereas the second can do the same underneath (I was searching for the correct english expression for this, but I don't remember it. Under the...? ^^ )

解决方案

foreach is a read only iterator that iterates dynamically classes that implement IEnumerable, each cycle in foreach will call the IEnumerable to get the next item, the item you have is a read only reference, you can not re-assign it, but simply calling item.Value is accessing it and assigning some value to a read/write attribute yet still the reference of item a read only reference.

这篇关于为什么我们不能分配一个 foreach 迭代变量，而我们可以用访问器完全修改它?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！