Hi, i had this little idea. when yo want to customize a class with a container like template <typename T, typename Container> struct Foo; then you must instanciate it with: Foo<int, std::vector<int> > the second int is redundant. --- Alternative: template <typename T, template <typename, typename> class Container> struct Foo; Here i do not have an allocator for the instantiation of Container. --- What i would like is: template <typename T, typename Container> struct Foo { typedef typename mpl::apply<Container, T>::type foo; }; and instantiate it with: Foo<int, mpl::stl_foo::vector<mpl::placeholder::_1> > For that i need namespace boost::mpl::stl_foo { template <typename T, typename Alloc> struct vector { typedef std::vector<T, Alloc> type }; } so i can curry containers as i wish. just an idea