Boost.TypeErasure docs say template const std::type_info & typeid_of(const any< Concept, T > & arg); [...] Requires: Concept includes typeid_<T>. T is a non-reference, CV-unqualified placeholder. which, if my literal reading is right, means that you can't use typeid_of on, say, any,_self&>, yet the following compiles on GCC #include #include #include #include <iostream> using namespace boost::type_erasure; int main() { int x=0; any,relaxed>,_self&> a=x; std::cout<