Rust also allows for non-thread safe reference-counted objects (Rc<>) that don't have the overhead of atomic instructions for updating the reference count. And it's getting support for custom local allocators, addressing the overhead of malloc/free. Along with a bunch of further advantages compared to C++ shared_ptr (such as being able to dispense with a pointer indirection in some cases, and allowing for sub-borrows that don't even need a refcount update because they can't possibly affect the 'ownership' of the object).