Is it even worth pointing out that the author misunderstands how UB works in Rust, given that at this point such a misunderstanding has to be willful than otherwise? There is _no_ UB in the safe subset of Rust, and in mixed safe-unsafe rust, the UB can only originate in the unsafe blocks.

In modern C++ (i.e. with smart pointers) something similar is true in that the UB can only occur in code dealing with certain types and functions (e.g. raw pointers), and not other types and functions. It's really the same as rust, just without the compiler support and the explicit unsafe blocks.

My understanding of UB is that in programming, there are corner cases which should be ignored by the language system. For example, C writing to a zero pointer is not “wrong”, you told it to write there when you dereferenced a zero pointer and assigned a value. The effects and the mitigation thereof just need to be outside the language, because otherwise you are saying that each and every memory access needs to be checked. So UB is just the language system saying “hey, I don’t know what happens, and we are not going to guarantee anything, and you can expect the world to explode if you do this, but not really, but yes really.”