Interior Mutability Design Pattern - Rust

int_mutability.rs

use std::rc::Rc;
use std::cell::RefCell;

trait Component {
    fn attach_to(&mut self, container: Rc<RefCell<Outer>>);
}

#[derive(Debug)]
struct Inner {
    cont: Option<Rc<RefCell<Outer>>>,
    ok: Option<String>,
}

impl Component for Inner {

    fn attach_to(&mut self, container: Rc<RefCell<Outer>>)
    {
        self.cont = Some(container);
        self.ok = Some("ATTACHED".to_string());
    }
}

#[derive(Debug)]
struct Outer {
    thing: Inner
}

impl Outer {
    
    fn new() -> Rc<RefCell<Self>> {
        let initial_value = Outer { thing: Inner { cont: None, ok: None }};
        let container = Rc::new(RefCell::new(initial_value));
        let thing = &mut container.borrow_mut().thing;
        
        thing.attach_to(container.clone());
        
        container.clone()
    }
}

fn main() {
   let wrapper = Outer::new();
   let outer = &mut wrapper.borrow_mut();
   println!("{:?}", outer.thing.ok);
   println!("{:?}", wrapper.as_ptr() == outer.thing.cont.as_ref().unwrap().as_ptr());
}