IIRC for a brief period GCC considered values outside of the enumeration as UB and heavily optimized according to this. At some point this interpretetion made i

IIRC for a brief period GCC considered values outside of the enumeration as UB and heavily optimized according to this. At some point this interpretetion made it as far as at least a draft standard. Then it got reverted as it went against decades of common usages and instead the opposite was made explicit in the standard. Making it UB for enum classes was considered, but the strongly typeded alias use case was considered safer and more useful.