By default, Rust just delegates to the ordinary libc malloc(), realloc(), and free(). In safe code, allocations are managed through RAII, just like in modern C+

By default, Rust just delegates to the ordinary libc malloc(), realloc(), and free(). In safe code, allocations are managed through RAII, just like in modern C++. Box works like unique_ptr, Arc works like shared_ptr, Vec works like vector, and so on. Lifetime annotations are just a way for the programmer to tell the compiler that none of the rules are being broken: they don't actually affect the semantics of the compiled program, they just make it fail to compile if there is an error. The underlying UB rules (except for those around unique references) are not much stricter than those required by C++; meanwhile, the lifetime rules are fairly strict, but the compiler cannot optimize based on them. At best, the lifetime system could allow you to use a faster design for your library, by placing tighter compile-time constraints on allowed use cases than you could have feasibly documented in a C++ library's interface. But examples of this are not too common in my experience, since most find it acceptable for C++ libraries not to accommodate sufficiently weird use cases.