Is modifying a value type from within a using statement undefined behavior?

Question

This one\'s really an offshoot of this question, but I think it deserves its own answer.

According to section 15.13 of the ECMA-334 (on the using statement,

Answer 1

I suspect the reason it compiles and runs is that SetField(int) is a function call, not an assignment or ref or out parameter call. The compiler has no way of knowing (in general) whether SetField(int) is going to mutate the variable or not.

This appears completely legal according to the spec.

And consider the alternatives. Static analysis to determine whether a given function call is going to mutate a value is clearly cost prohibitive in the C# compiler. The spec is designed to avoid that situation in all cases.

The other alternative would be for C# to not allow any method calls on value type variables declared in a using statement. That might not be a bad idea, since implementing IDisposable on a struct is just asking for trouble anyway. But when the C# language was first developed, I think they had high hopes for using structs in lots of interesting ways (as the GetEnumerator() example that you originally used demonstrates).