AMDG Ares Lagae wrote:

I have a base class template "template struct base {};" and a derived class "derived" that publicly derives from several instantiations from the base class template.

Given a type "T1", is it possible to decide if the class "derived" is derived from a base "base" and deduce the unknown type "X"?

I couldn't think of a way to do this without typeof. (At least without enumerating all the possible first template arguments) #include #include #include #include namespace mpl = boost::mpl; struct no { typedef void type; }; template<class U> struct wrap { no dummy[2]; typedef U type; }; template struct X {}; template struct derives_from_X { private: template<class U2> static wrap<U2> test(X*); static no test(...); BOOST_TYPEOF_NESTED_TYPEDEF_TPL(nested, test((T*)0)); typedef typename nested::type result; public: typedef typename result::type template_argument; typedef mpl::bool_ type; enum { value = type::value }; }; struct tester : X, X {}; int main() { BOOST_MPL_ASSERT((derives_from_X)); BOOST_MPL_ASSERT((boost::is_same::template_argument, char>)); BOOST_MPL_ASSERT((derives_from_X)); BOOST_MPL_ASSERT((boost::is_same::template_argument, double>)); } In Christ, Steven Watanabe