Edit RefCell in closure - rust

Question

I want to store a closure in struct that implements Clone, so i'm code this:
use std::rc::Rc;
type Closure = Box<dyn Fn() -> ()>;
#[derive(Clone)]
struct A {
closure: Option<Rc<Closure>>,
}
impl A {
pub fn new() -> A {
A { closure: None }
}
pub fn closure(&self) -> Option<Rc<Closure>> {
self.closure.clone()
}
pub fn set_closure(&mut self, closure: Closure) -> &mut Self {
self.closure = Some(Rc::new(closure));
self
}
}
fn main() {
let mut a: A = A::new();
a.set_closure(Box::new(|| -> () { println!("Works fine!") }));
(a.closure().unwrap())();
}
Now I want to test this code by borrowing a variable of current scope. It's important to keep a reference in main function, because i need to use it after.
I code this:
use std::cell::RefCell;
fn main() {
let mut a: A = A::new();
let value: Rc<RefCell<i8>> = Rc::new(RefCell::new(0));
println!("Value = {}", value.borrow());
a.set_closure(Box::new(|| -> () {
*value.borrow_mut() = 1;
}));
(a.closure().unwrap())();
println!("New value = {}", value.borrow());
}
But I get this error:
Compiling playground v0.0.1 (/playground)
error[E0597]: `value` does not live long enough
--> src/main.rs:34:38
|
34 | a.set_closure(Box::new(|| -> () { *value.borrow_mut() = 1; }));
| ---------------------^^^^^---------------------
| | | |
| | | borrowed value does not live long enough
| | value captured here
| cast requires that `value` is borrowed for `'static`
...
38 | }
| - `value` dropped here while still borrowed
Would anyone know what I need to do please.
Thank you for your reply in advance.

Answer 1

Rcs are shared by cloning, which increments their reference count. But you pass a reference to it to the closure, which is perhaps defeating the point of using an Rc in the first place. As the error says, the closure is holding a reference to value after value is dropped.
You probably intended to write something like this, which clones the Rc and moves the clone into the closure:
let cloned_value = value.clone();
a.set_closure(Box::new(move || *cloned_value.borrow_mut() = 1));
Or (my preference) avoiding introducing a new binding in the outer scope:
a.set_closure(Box::new({
let value = value.clone();
move || *value.borrow_mut() = 1
}));