[josephg]

I don’t know what you’re referring to. Unsafe seems pretty well defined for 99% of use cases. Unsafe blocks allow you to dereference raw pointers and call unsafe functions. Thats about it. Remarkably, even in codebases which need a lot of unsafe (eg the kernel), almost all code is safe code.

[afiori]

What I mean is that unsafe code allows you to eg break std invariants (set invalid length to Vec, unlock a locked mutex, etc.) in ways that can be UB, which of these are UB and which can be used "safely" is sort of unknown.

For better or worse they are much more well understood in C as they are front and center of the language semantics