abbreviation for reference counting

Cloning an Rc<T> Increases the Reference Count

enum List {
    Cons(i32, Rc<List>),
use crate::List::{Cons, Nil};
use std::rc::Rc;
fn main() {
    let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil)))));
	 println!("count after creating a = {}", Rc::strong_count(&a)); // 1
    let b = Cons(3, Rc::clone(&a));
	println!("count after creating b = {}", Rc::strong_count(&a)); // 2
    let c = Cons(4, Rc::clone(&a));

The implementation of Rc::clone doesn’t make a deep copy of all the data like most types’ implementations of clone do. The call to Rc::clone only increments the reference count, which doesn’t take much time.