https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102092
--- Comment #3 from David Friberg <davveston at gmail dot com> ---
(In reply to David Friberg from comment #2)
> I believe your program has UB as it contains an odr-violation due to the
> friend declaration of the stream operator function , as its in-class
> definition ("hidden friend") makes use of the non-type template parameter
> 'Degree'.
>
> The hidden friend, albeit being inline (protection against multiple-TU
> odr-violations, given token-by-token identical definitions), will have
> multiple definitions that are not the same as soon as two specializations of
> the class template 'Polynomial' are instantiated if these two
> specializations differ in the 'Degree' template parameter.
>
> Recall that a non-template friend of a class template is in itself not a
> templated entity, but a namespace-scope function.
Never mind, I realized the hidden friend uses the class template as an
argument, though, so each specialization will instantiate a separate overload,
so I guess there will be no odr-violation Nafter all.
