operator class&() { return *this; } considered harmful?

I was wondering if there were any serious gotchas with including a
conversion to class& in a class's public interface.

Consider

#include <iostream>
using namespace std;

class C {
   int fld;
public:
   C(int x) : fld(x) {}
   C(const C &r) : fld(r.fld) {}
   int get_val() { return fld; }
   operator C&() { return *this; }
};

C f()
{
   C temp(2);
   return temp;
}

int main()
{
   C &x = f();
   cout << "x = " << x.get_val() << endl;
   return 0;
}

Without the operator C&, I can't initialise the reference x in main
(by 8.5.3, para 5). But with it in place, it seems to me as if the
language in 12.2 para 5 then guarantees that the object nominally
allocated in f will actually have a lifetime equivalent to the scope
of main's body.

But maybe there's something I'm missing?

Thanks,
Michael.

---
[ comp.std.c++ is moderated. To submit articles, try just posting with ]
[ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ]
[ --- Please see the FAQ before posting. --- ]
[ FAQ: http://www.comeaucomputing.com/csc/faq.html ]