Adam Badura:
2)
Non-standard exceptions derived from standard exceptions are sliced by current_exception. It detects those types by throwing and caching and thus will catch also derived types (like null_pointer : public std::invalid_argument). But during construction of internal structures the standard exception type is used and thus copy construction slices the original exception object. If typeid was used instead of throwing/catching (or dynamic_cast) to detect the type current_exception could at least detect that is will slice the original object and use a different type so it would not pretend everything is OK.
What would you gain from that? If you catch(invalid_argument) you want null_pointer to be caught; if current_exception translated it to something else, it wouldn't be. current_exception can store something derived from invalid_argument, but what are the benefits of doing so? Either way, catching an invalid_argument works, catching a null_pointer doesn't.