https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70347
--- Comment #1 from Zhihao Yuan <lichray at gmail dot com> --- In c++1y, c++14 modes, not c++11.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70347
--- Comment #1 from Zhihao Yuan <lichray at gmail dot com> --- In c++1y, c++14 modes, not c++11.