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From: "f.heckenbach@fh-soft.de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/94061] defaulted member operator <=> defined as deleted if
 a base has protected member operator <=>
Date: Sat, 08 Jan 2022 21:59:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94061

--- Comment #3 from Frank Heckenbach <f.heckenbach@fh-soft.de> ---
(In reply to Patrick Palka from comment #2)
> How do you define it?  It works if we define it as
>=20
>   auto operator <=3D> (const B& b) const {
>     return A::operator<=3D>(b);
>   }
>=20
> but not if it's defined as
>=20
>   auto operator <=3D> (const B& b) const {
>     return static_cast<const A&>(*this) <=3D> static_cast<const A&>(b);
>   }

I'd do the former. I don't know what the standard says exactly, but intuiti=
vely
it seems to me that "protected" should suffice, also by comparison with
constructors.=