[Bug libstdc++/87855] std::optional<T> only copy-constructible if T is trivially copy-constructible

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87855

--- Comment #14 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
(In reply to fiesh from comment #12)
> X(double) : X(X(42)) {} // clang doesn't like this
> 
> is also enough to show the difference, no need for an operator.

Yeah. The list-archive link that you probably can't open leads to
Richard's explanation why copy elision should not happen with
delegating constructors. That's the bug, not the lack of deletedness
of the union's copy constructor.