On Thu, 31 Oct 2024 at 15:24, Fiodar <fedor_qd@xxxxxxx> wrote: > > > It doesn’t say why. > > Compare two GCC reports: > error: must be a non-static member function > and > warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister] > > More clear error message as for me may be: > error: ISO C++ does not allow non-static member function 'R* operator->(const R&)' GCC only uses the "ISO C++ does not allow ..." form for rules that are modified by GCC extensions. So for -Wregister it's telling you that the keyword is allowed by GCC, but is not allowed by ISO C++. For the first case, it's never allowed. It's not valid in ISO C++ and it's not valid in GNU C++. So I disagree with your suggestion. It would be confusing and inconsistent to say "ISO C++ does not allow ..." for something that is never allowed by any form of C++. It's not allowed by ISO C++, or GNU C++, or traditional 1990s C++ before there was a standard. > Yes, I already know why that operator must be that. https://en.cppreference.com/w/cpp/language/operators If the compiler says something is not allowed, you should assume it's because the language rules don't allow it. That's how compilers work.
