In C#, why can't I modify the member of a value type instance in a foreach loop?

Question

I know that value types should be immutable, but that\'s just a suggestion, not a rule, right? So why can\'t I do something like this:

struct MyStruct
{
             


        

Answer 1

Value types are called by value. In short, when you evaluate the variable, a copy of it is made. Even if this was allowed, you would be editing a copy, rather than the original instance of MyStruct.

foreach is readonly in C#. For reference types (class) this doesn't change much, as only the reference is readonly, so you are still allowed to do the following:

    MyClass[] array = new MyClass[] {
        new MyClass { Name = "1" },
        new MyClass { Name = "2" }
    };
    foreach ( var item in array )
    {
        item.Name = "3";
    }

For value types however (struct), the entire object is readonly, resulting in what you are experiencing. You can't adjust the object in the foreach.