https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67537
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
My first impression is that this is a clang bug.
This:
template<typename... _UElements> using _TMC =
_TC<(sizeof...(_Elements) == sizeof...(_UElements)),
_Elements...>;
should make it impossible to get:
/home/trippels/gcc_6/usr/local/lib/gcc/powerpc64le-unknown-linux-gnu/6.0.0/../../../../include/c++/6.0.0/tuple:481:62:
error: pack expansion contains parameter packs
'_Elements' and '_UElements' that have different lengths (1 vs. 0)
return __and_<is_constructible<_Elements, _UElements&&>...>::value;
~~~~~~~~~ ~~~~~~~~~~ ^
/home/trippels/gcc_6/usr/local/lib/gcc/powerpc64le-unknown-linux-gnu/6.0.0/../../../../include/c++/6.0.0/tuple:580:21:
note: in instantiation of function template
specialization 'std::_TC<true, boost::hana::test::integer<0, 17, void>
>::_MoveConstructibleTuple<>' requested here
_MoveConstructibleTuple<_UElements...>()
^
because it should not be possible for _Elements and _UElements to have
different lengths inside _TC<true, ...>, it should have gone to _TC<false, ...>
instead.
