I believe this is a gcc bug.
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79094

Tom.

On 8/23/19 7:01 AM, Vladimir Grigoriev via Std-Discussion wrote:
> This program
>
> #include <iostream>
>
> template <typename ...Bases>
> struct S : Bases...
> {
> using Bases::Bases...;
> };
>
> int main()
> {
> }
>
> does not compile using gcc HEAD 10.0.0 20190
> <https://wandbox.org/#compiler-tab-33>.
>
> The error message is
>
> rog.cc:6:23: error: parameter packs not expanded with '...':
> 6 | using Bases::Bases...;
> | ^~~
> prog.cc:6:23: note: 'Bases'
>
> However it compiles using Clang HEAD 9.0.0.
>
> So the question is Is it a valid using declaration or is there a gcc bug?
>
> With best regards,
> Vlad from Moscow
>
> You can meet me at http://cpp.forum24.ru/ or www.stackoverflow.com or
> http://ru.stackoverflow.com
>