A little closer would be to use a shared_ptr<X> and shared_ptr<Y> that share the same reference count (1). It's not exactly the same thing, though, since Rust gives you some safe usage checks that you don't get with shared_ptr. That is, vanilla Rust objects have lifetime semantics closer to unique_ptr than shared_ptr.

(1): See constructor number 7 here, which was designed for this purpose: http://en.cppreference.com/w/cpp/memory/shared_ptr/shared_pt...