Or you can just trust the language. And if its not right, or not the way you plan to use it, what then? You're stuck unless the language also permits you to roll your own.
Rust does allow you to implement low-level things in itself, by giving an escape hatch into C/C++-like unsafe code (i.e. risk-of-incorrectness is purely opt-in, rather than always-there).
Examples of things efficiently implemented entirely in the standard library in pure Rust (well, with some calls into the operating system/libc): Vec, the std::vector equivalent. Rc, reference counted pointers (statically restricted to a single thread). Arc, thread-safe reference counted pointers. Mutex. Concurrent queues. Hashmap.
