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

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

#[allow(unused_variables)]
fn main() {
    let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil)))));
    let b = Cons(3, Rc::clone(&a));
    let c = Cons(4, Rc::clone(&a));
    println!("The total references in a: {}", Rc::strong_count(&a));
    // println!("The total references in b: {}", Rc::strong_count(&b));
    // the above statement only works with Rc::new, but b is
    // b is a list
    {
        let d = Cons(10, Rc::clone(&a));
        println!("The total references for a: {}", Rc::strong_count(&a));
    }
    println!("The total references in a: {}", Rc::strong_count(&a));

}