I think one of the fundamental differences in the SOTA C++ approach to memory safety (eg. extending unique/shared_ptr) and Rust is that C++ doesn't try to enfor

I think one of the fundamental differences in the SOTA C++ approach to memory safety (eg. extending unique/shared_ptr) and Rust is that C++ doesn't try to enforce having a single mutable reference to a variable and it still relies on strict aliasing heuristics, and so cannot claim to be fully deterministic. Still, use after free, and memory leaks should be impossible. It'll still let you do a bunch of stuff Rust doesn't, which is up to the programmer to decide whether this is good or not.