https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58407
--- Comment #18 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Steinar H. Gunderson from comment #17) > Base needs to have a virtual destructor since it has virtual member > functions (or half the world will give you warnings). Or a protected destructor, but that doesn't change anything relevant to your problem. > Any attempts now to copy Derived through the implicit copy constructor will > give a warning, since the synthesis of Base::Base(const Base &) is > deprecated. The only way I've found to suppress this is to add > > Base::Base(const Base &) = default; > > However, this in turn disables the synthesis of Base::Base(), and also > Base::operator=(const Base &). So I need: > > Base() = default; > Base(const Base &) = default; > Base(Base &&) = default; > Base &operator= (const Base &) = default; > Base &operator= (Base &&) = default; > > for something that doesn't have a single member! Yes. The deprecation means a future version of C++ might make your type non-copyable. To explicitly say it's copyable (and make the code futureproof) you need to add those defaulted members. If you don't want to do that, you can use -Wno-deprecated-copy to suppress the warnings.
