Why does decltype(*this) not return the correct ty

问题:

The following code was compiled with VC++ Nov 2012 CTP. But the compiler gave a warning.

I just wonder whether this is a bug of VC++ Nov 2012 CTP.

struct A
{
    int n;

    A(int n)
        : n(n)
    {}

    int Get() const
    {
        return n;
    }

    int Get()
    {
        //
        // If using "static_cast<const A&>(*this).Get();" instead, then OK.
        //
        return static_cast<const decltype(*this)&>(*this).Get(); // Warning!
    }
};

int main()
{
    A a(8);

    //
    // warning C4717: 'A::Get' : recursive on all control paths,
    // function will cause runtime stack overflow
    //
    a.Get(); 
}

回答1:

decltype applied to an expression that's not an id-expression gives you a reference, so decltype(*this) is already A&, and you can't make that const again. If you really wanted to use decltype, you could do something like this:

static_cast<std::decay<decltype(*this)>::type const &>(*this)

Or even this:

static_cast<std::add_lvalue_reference<
                 std::add_const<
                      std::decay<decltype(*this)>::type
                 >::type
            >::type
>(*this)

Of course it's much simpler to just say static_cast<A const &>(*this).