https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99985
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
We can still make it short circuit (and so not instantiate class templates
unnecessarily) like this:
#if __cplusplus <= 201402L
return __and_<__bool_constant<_No_realloc>,
is_nothrow_copy_constructible<_Hash>,
is_nothrow_copy_constructible<_Equal>>::value;
#else
if constexpr (_No_realloc)
if constexpr (is_nothrow_copy_constructible<_Hash>())
return is_nothrow_copy_constructible<_Equal>();
return false;
#endif
I didn't use __and_<> because that has to be instantiated too (although it's
cheaper than the is_xxx_constructible ones), and for C++17 the if-constexpr
version avoids that. But if we need a #if to work for C++11 anyway, we might as
well use __and_ for C++11 and C++14, and if-constexpr for everything later.
