https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102995
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Are you sure this is valid? Both ICC and MSVC reject it for the same reason as GCC. Can a friend of First<A, B> be made a friend of First<B, C> via the friend, I don't think so?