[Bug libstdc++/117858] [15 regression] std::optional with a constructor template ctor(T)

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117858

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
N.B. it's also more maintainable using concepts, so that future changes will be
easier to implement.