The Rust Book has an example: https://doc.rust-lang.org/book/ch15-06-reference-cycles.html

Of course, leaking memory is as easy as using `Box::leak`, although that's probably never going to happen accidentally.

You could store a `RefCell<Option<T>>` in an `Rc` and set it to `Some(rc)` after creation.

Or you could use the recently-stabilized `new_cyclic` method: https://doc.rust-lang.org/std/rc/struct.Rc.html#method.new_c...

And when using C libraries / FFI, there are a lot of tricky things going in, it is much easier to leak in unsafe land.