IIRC there have been actual proposals, which also incorporated setting a compile mode, e.g. safe mode, which got easier to implement/standardize after the introduction of modules compared to the include model. But I cannot find those proposals now.   -----Ursprüngliche Nachricht----- Von:Mehmet Kayaalp via Std-Proposals <std-proposals_at_[hidden]> Gesendet:So 27.11.2022 18:12 Betreff:Re: [std-proposals] Pragmas using multiple C++ standards within the same project An:std-proposals_at_[hidden]; CC:Mehmet Kayaalp <mehmet.kayaalp_at_[hidden]>;  I would say the features that might go to the chopping block would be (1) those that are strongly discouraged from using and (2) those that make the life of a modern compiler designer horrible—I suspect your options C­ through F may be the closest ones to the criteria above. -----Ursprüngliche Nachricht----- Von:Sebastian Wittmeier <wittmeier_at_[hidden]> Gesendet:So 27.11.2022 00:48 Betreff:AW: [std-proposals] Pragmas using multiple C++ standards within the same project CC:Mehmet Kayaalp <mehmet.kayaalp_at_[hidden]>; An:std-proposals_at_[hidden];   C) Features, which are not recommended for modern C++ like C arrays   D) Features, which are not recommended for user code like new/delete (instead of smart pointers) - i.e. introducing different code levels like system/library/user   E) Parser difficulties like Most Vexing Parse or comma-operator for multi-dimensional arrays   F) Bad historic language defaults, e.g. user-defined constructor should automatically delete copy constructor and copy assignment operator or one-argument constructors should not do implicit conversion