Hi, cvs head can't compile this. #include <boost/fusion/include/as_vector.hpp> #include <boost/fusion/include/transform_view.hpp> #include <boost/fusion/include/vector.hpp> struct identity { template<class FunCall> struct result; template<class Fun> struct result<Fun(int&)> { typedef int& type; }; int& operator()(int& i) const { return i; } }; int main() { typedef boost::fusion::vector<int, int> from_t; from_t from; boost::fusion::transform_view<from_t, ::identity> v(from, ::identity()); // error. boost::fusion::as_vector(v); } fusion::as_vector calls result_of::value_of. Then, <boost/fusion/sequence/view/transform_view/detail/value_of_impl.hpp> calls result_of::value_of. So, non-reference int is passed to ::identity::result. I'm not sure which is wrong, as_vector or transform_view. Regards, -- Shunsuke Sogame