https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85222
--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Seems simpler to just define:
struct __dual_ios_failure {
__dual_ios_failure(std::string s, error_code e) : new_(s, e), old_(s) { }
ios::failure[abi:cxx11] new_;
ios::failure old_;
};
and make __throw_ios_failure() throw one of that type, and make the EH runtime
do the necessary adjustments to make this work:
__dual_ios_failure * p1;
try {
try {
try {
throw __dual_ios_failure("", {});
} catch (__dual_ios_failure& e1) {
p1 = &e1;
throw;
}
} catch (ios::failure[abi:cxx11]& e2) {
assert( &e2 == &p1->new_ );
throw;
}
} catch (ios::failure& e3) {
assert( &e3 == &p1->old_ );
}
i.e. if the catch handler is one of the ios::failure types and the actual
thrown exception is __dual_ios_failure then catch the member instead of the
object itself. The "throw;" would re-throw the original object of type
__dual_abi_failure, so the next handler would be able to perform the same
checks and adjustments.
This would only require magic in the EH catch routines, not a new way to
declare base classes.
