https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107065
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Or as a compile-time test, not run-time:
template<class, class> struct is_same { static constexpr bool value = false; };
template<class T> struct is_same<T,T> { static constexpr bool value = true; };
int main() {
bool b = true;
static_assert( is_same<decltype(!(!b)), bool>::value, "");
auto bb = (!(!b));
static_assert( is_same<decltype(bb), bool>::value, "");
}
<source>: In function 'int main()':
<source>:5:52: error: static assertion failed
5 | static_assert( is_same<decltype(!(!b)), bool>::value, "");
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
