[Bug c++/59498] [DR 1430][4.9/5/6/7 Regression] Pack expansion error in template alias

[ldionne.2 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59498

--- Comment #12 from Louis Dionne <ldionne.2 at gmail dot com> ---
Not sure, as I've been off pure-type computations for a while now. Looking at
how Meta does it might be useful:
https://github.com/ericniebler/meta/blob/master/include/meta/meta.hpp#L819