reference count

refcount.rs

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

struct A {
	value: Rc<RefCell<Vec<i64>>>,
}

struct B {
	value: Rc<RefCell<Vec<i64>>>,
}

impl A {
	fn new(mut v: Vec<i64>) -> A {
		A {
			value: Rc::new(RefCell::new(v))
		}	
	}
}

impl B {
	fn new(mut v: Rc<RefCell<Vec<i64>>>) -> B {
		B { value: v }
	}
}

impl Drop for A {
	fn drop(&mut self) {
		println!("dropping A");
	}
}

impl Drop for B {
	fn drop(&mut self) {
		println!("dropping B");
	}
}


fn main() {
	let a = A::new(Vec::new());
	a.value.borrow_mut().push(20);
	let mut b = Some(a.value.clone());
	b.unwrap().borrow_mut().push(30);
	println!("Hello, world!");


	{
		let b2 = B::new(a.value.clone());

		b2.value.borrow_mut().push(40);
		b2.value.borrow_mut().push(200);

	}

	b = None;
	let c3 = a.value.clone();
	c3.borrow_mut().push(100);
	println!("reference count: {}", Rc::strong_count(&a.value));
}