'warning C4709: comma operator within array index expression' - but no comma to be seen anywhere!

Question

Take this little example code:

struct Test{
    operator int() const{
        return 0;
    }
};

Test test(){
    return Test();
}

int main(){
    int arr[10];
    arr[test()] = 5;
}

Compiling under Visual Studio 2010 with /W4 generates said warning. Interestingly, if I add but a simple default constructor, the warning suddenly vanishes. Also, it only works in that constellation. If I remove the function call or don't return a user-defined type, the warning disappears. Also, as expected, GCC doesn't produce such a warning.

So, can I take this warning with the above code as a bug in Visual Studio or is there more to it than seems? Would be very surprising though, to say the least.

---

Edit: Created a bug report on Microsoft Connect.

Answer 1

Definitely it is a bug - misleading warning.