(Note: The following contribution is essentially a copy of a former one, which was, due to several administrative problems on my side, probably overlooked by the majority of concerned programers) Dear Boosters, its quite a while that I could participate in this newsgroup, so maybe my request is ol' stuff and has been answered 100 times. In case of that I apologize for the following question: I observe that boost::tuple::length in version 1.32+1.33RC2 exist two template specializations for empty tuples, namely template<> struct length<tuple<> > { BOOST_STATIC_CONSTANT(int, value = 0); }; template<> struct length<null_type> { BOOST_STATIC_CONSTANT(int, value = 0); }; which lead to the unexpected effect that e.g. typedef const tuple<> ConstEmptyTuple; int k = length<ConstEmptyTuple>::value; (modulo namespace issues) does not compile. The reason is obvious, because deduction of boost::tuples::length<ConstEmptyTuple> extracts "const tuple<>", which leads to the generic template definition: template<class T> struct length { BOOST_STATIC_CONSTANT(int, value = 1 + length<typename T::tail_type>::value); }; which does not compile in this case, because const oost::tuples::tuple<> has no tail_type. Similar situations arise for const null_type arguments and corresponding volatile variants thereof. To my humble opinion tuples::length should work independent of cv qualification of the template arguments, but this route should of course be gone in accordance to similar situations of "template predicates" in boost::mp/type_traits. One further indirection and usage of boost::remove_cv<T> could simply resolve the described problem, such as: // Define length_impl + 2 specialisation for tuple<> and null_type as // currently done for length namespace details { template <typename T> struct length_impl { .. // as before; }; template <> struct length_impl<null_type> { .. // as before; }; template <> struct length_impl<tuple<null_type, ...> > { .. // as before; }; } // One single - not specialized - length template handling all cases: template <typename T> struct length { static const int value = details::length_impl< typename ::boost::remove_cv<T>::type >::value; }; What do you think? Greetings from Bremen, Daniel Krügler