Here is a generic exception_ptr implementation based on a registry of exception types. (http://joshuanapoli.com/exception/) The registry is built at runtime. boost::throw_exception can register the thrown type. current_exception() searches for the most derived type in the registry that matches the current exception. (http://joshuanapoli.com/exception/jn/boost/exception/detail/emulate_exc eption_ptr.hpp)
If boost::throw_exception is modified such that its postcondition is that the exception object it throws derives from boost::exception (I can't think of a reason not to), cloning can be implemented intrusively without a need for registration. A run-time registry maintained by boost::throw_exception could cause problems in multi-threaded environments, as well as in the presence of DLLs (consider that if a DLL is unloaded, any std::type_info object obtained from it becomes invalid, so it can not be used safely as a key in the registry.) -- Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode