Rust編程進階：042、樹形結構2

例子：

use std::cell::RefCell;
use std::rc::{Rc, Weak};

#[derive(Debug)]
struct Node {
    value: i32,
    parent: RefCell<Weak<Node>>,
    children: RefCell<Vec<Rc<Node>>>,
}

fn main() {
    let leaf = Rc::new(Node {
        value: 3,
        parent: RefCell::new(Weak::new()),
        children: RefCell::new(vec![]),
    });
    println!(
        "1 leaf strong = {}, weak = {}",
        Rc::strong_count(&leaf),
        Rc::weak_count(&leaf)
    );
    {
        let branch = Rc::new(Node {
            value: 5,
            parent: RefCell::new(Weak::new()),
            children: RefCell::new(vec![Rc::clone(&leaf)]),
        });
        println!(
            "1 branch strong = {}, weak = {}",
            Rc::strong_count(&branch),
            Rc::weak_count(&branch)
        );

        *leaf.parent.borrow_mut() = Rc::downgrade(&branch);
        println!(
            "2 branch strong = {}, weak = {}",
            Rc::strong_count(&branch),
            Rc::weak_count(&branch)
        );

        println!(
            "2 leaf strong = {}, weak = {}",
            Rc::strong_count(&leaf),
            Rc::weak_count(&leaf)
        );
    }

    // println!(
    //     "3 branch strong = {}, weak = {}",
    //     Rc::strong_count(&branch),
    //     Rc::weak_count(&branch)
    // );

    println!(
        "3 leaf strong = {}, weak = {}",
        Rc::strong_count(&leaf),
        Rc::weak_count(&leaf)
    );
}

本節全部源代碼：
https://github.com/anonymousGiga/learn_rust/blob/master/learn_weak2/src/main.rs