https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67991
--- Comment #4 from Jacob McIntosh <nacitar at ubercpp dot com> --- It looks like this is supposed to be a c++1y/1z feature (post c++-14 anyway)... and it looks like it's not implemented yet in gcc. Same errors for me with -std=c++1y and also with -std=c++1z
