https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81507
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- /home/bebuch/media/programme/gcc-7/include/c++/7.1.1/tuple:1670:44: required from 'constexpr decltype(auto) std::apply(_Fn&&, _Tuple&&) [with _Fn = const std::vector<int>&; _Tuple = long unsigned int]' ^^^ there's your hint. It tells you that std::apply was called.
