Who reads the "manual of C++" -- what even is that, the standard document (certainly no-one should read that for learning). It would be just about OK for the c

Who reads the "manual of C++" -- what even is that, the standard document (certainly no-one should read that for learning). It would be just about OK for the compiler to refuse to compile X and Y together. If you "switched off" X, then in C++ (where code is in headers which are just concatenated with your code), this would effectively split the language, as you also couldn't use libraries which use X in their headers.