More generally, with C you can't restrict what can (accidentally or not) interact with the internal unsafe bits (without the cost of forcing the data to always

More generally, with C you can't restrict what can (accidentally or not) interact with the internal unsafe bits (without the cost of forcing the data to always live in the heap at least; or perhaps annoying field names that are automatically searched-for by your build system, though then you're essentially making a DSL), or even force using the "safe" parts properly (not enforced at compile-time, at least) outside of, again, a rather limited subset of cases. As a very general example, you can repeat basically any statement in C twice and it'll still compile. If you get lucky, the compiler might tell you you've ended up with a double-free or something, but that's a very limited set of cases, and won't help if the second copy is invoked down a couple function calls. There may be some ways to still get additional true guarantees in C, but they'll be rather more restrictive than ones you can write in Rust, and you'll likely end up with overhead, which tempts skimping out on doing things properly in the name of performance.