In Rust, using smart pointers is not much of an "explicit choice" - it's simply the idiomatic thing to do when something might be kept around by more than one p

In Rust, using smart pointers is not much of an "explicit choice" - it's simply the idiomatic thing to do when something might be kept around by more than one parent object. Rc<T> basically means that there are multiple sources of control over T's lifetime, but these are all within a single thread; and Arc<T> signals that the control might extend to multiple threads. It's not "mere implementation" that we're dealing with here; it's the very semantics of the code as it relates to Rust's expanded take on the well-known RAII pattern. Swift simply lacks an equivalent to either the Rc<> specifier or e.g. Rust's Box<>, which expresses the semantics of an object which is heap-allocated and accessed via an indirection, and verifiably has at all times a unique "owner" controlling its lifetime (as per usual RAII).