Longtime C, C++, and embedded programmer here.

1. Why "should" it be something different? It is semantically part of code flow; making it a pragma breaks that model. This replaces the nonstandard __builtin_unreachable().

2. This doesn't exist to save typing. static_cast<auto> doesn't make sense to me (that reads like a no-op). static_cast<underlying> introduces a new reserved word which is a big no-no.

3. This is not the same as htonl, which only does anything on little-endian machines. (htonl is also a POSIX function, not a C++ function.)