Do rvalue references to const have any use?

Question

I guess not, but I would like to confirm. Is there any use for const Foo&&, where Foo is a class type?

Answer 1

They are occasionally useful. The draft C++0x itself uses them in a few places, for example:

template <class T> void ref(const T&&) = delete;
template <class T> void cref(const T&&) = delete;

The above two overloads ensure that the other ref(T&) and cref(const T&) functions do not bind to rvalues (which would otherwise be possible).

Update

I've just checked the official standard N3290, which unfortunately isn't publicly available, and it has in 20.8 Function objects [function.objects]/p2:

template <class T> void ref(const T&&) = delete;
template <class T> void cref(const T&&) = delete;

Then I checked the most recent post-C++11 draft, which is publicly available, N3485, and in 20.8 Function objects [function.objects]/p2 it still says:

template <class T> void ref(const T&&) = delete;
template <class T> void cref(const T&&) = delete;