It applies to the enum. If you couldn’t lift an integer into the enum without branching, then the enum isn’t zero cost - it requires more resources than C would

It applies to the enum. If you couldn’t lift an integer into the enum without branching, then the enum isn’t zero cost - it requires more resources than C would to do the same thing. Bounds checking is never mandatory in C++. When C++ has broken this rule, developers have tended to turn those features off or ban them in style guides.