Indeed, some uses of unsafe aren't meaningfully factorable. File backed memory maps or shared memory with other processes are other important real world example

Indeed, some uses of unsafe aren't meaningfully factorable. File backed memory maps or shared memory with other processes are other important real world examples that are difficult or impossible to meaningfully factor in the context of a single process. But I still think that saying "safety in Rust is factorable" is accurate beyond a mere first approximation. Figuring out how to encapsulate unsafety is, in my experience, the essential creative aspect to using unsafe at all. Because if safety wasn't something you could encapsulate, then Rust really wouldn't be what it is. (I have spent many long hours thinking about how and to what extent the safety of file backed memory maps could be encapsulated. Which is to say, factoring safety is really the ultimate goal, even if certain things remain beyond that goal.)