Possible defect: enum with fixed underlying type - undefined behavior with out of range values

[shmuel...@gmail.com]

1. The underlying type is not required to be able to represent all of the enum values.
2.  An unrepresentable value can occur in some cases, for example: 

 enum foo : bool { True=true, undefined }

See: https://stackoverflow.com/questions/39621098/what-happens-if-an-enum-cannot-fit-into-an-unsigned-integral-type