Code shared from the Rust Playground

playground.rs

use std::rc::Rc;
use std::cell::RefCell;
use List::{Cons, Nil};

#[derive(Debug)]
enum List {
  Cons(i32, RefCell<Rc<List>>),
  Nil,
}

impl List {
  fn tail(&self) -> Option<&RefCell<Rc<List>>> {
    match *self {
      Cons(_, ref item) => Some(item),
      Nil => None,
    }
  }
}


fn main() {
  
  let a = Rc::new(Cons(5, RefCell::new(Rc::new(Nil))));

  println!("a initial rc count = {}", Rc::strong_count(&a));
  println!("a next item = {:#?}", a.tail());
  
  let b = Rc::new(Cons(10, RefCell::new(Rc::clone(&a))));
  println!("a initial rc count after b creation = {}", Rc::strong_count(&a));
  println!("b initial rc count = {}", Rc::strong_count(&b));
  println!("b next item = {:#?}", b.tail());
  
  if let Some(link) = a.tail() {
      *link.borrow_mut() = Rc::clone(&b);
  }
  
  println!("b rc count after changing a = {}", Rc::strong_count(&b));
  println!("a rc count after changing a = {}", Rc::strong_count(&a));
  
  //println!("a next item = {:#?}", a.tail());
}