[Boost-users] Using MPL to write is_derived_from_std_basic_ostream

I'm trying to ascertain whether a given class is, or is derived from, std::basic_ostream, but I've ground to a halt. The attached code successfully reports those classes that do derive from std::basic_ostream but fails to compile when I test std::string, bool, char etc. I can see what is going wrong, but have run out of ideas about how to fix it. I'm also painfully aware that my attempts are just plain ugly. Can someone show me the way forward? Regards, Angus