c# - Why can't we assign a foreach iteration variable, whereas we can completely modify it with an accessor?

Question

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...? ^^ )

Answer 1

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.