smart-pointers

enum List {
    Cons(i32, Box<List>),
    Nil,
}

use List::{Cons, Nil};

use std::ops::Deref;

struct MyBox<T>(T);

impl<T> Deref for MyBox<T> {
    type Target = T;

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

fn main() {
    let data = Rc::new(RefCell::new(vec![1, 2, 3]));