Hmm... I had the impression that it's impossible to register default-parameter-versions of forward-declared templates. But this impression was caused by my experience with STL registration, where all default parameters are provided in the class definitions, and I was obviously not able to change this. But it looks possible to specify them in the declarations (verified with vc71, gcc, and comeau online), so the following code is compiles: --------------------------------------------- #define BOOST_TYPEOF_COMPLIANT #include <boost/typeof/typeof.hpp> template<class T, class U = T*, class V = U*> struct x; #include BOOST_TYPEOF_INCREMENT_REGISTRATION_GROUP() BOOST_TYPEOF_REGISTER_TEMPLATE(x, 1) BOOST_TYPEOF_REGISTER_TEMPLATE(x, 2) BOOST_TYPEOF_REGISTER_TEMPLATE(x, 3) template<class T, class U, class V> struct x {}; typedef BOOST_TYPEOF(x<int>()) type1; typedef BOOST_TYPEOF((x<int, short>())) type2; typedef BOOST_TYPEOF((x<int, short, char>())) type3; int main() {} --------------------------------------------- If this code is portable, I would say it definitely seems more preferable for default parameter registrations than anything we discussed so far. Regards, Arkadiy