What is the right way to share a reference between closures if the value outlives the closures?

Question

I want to share a reference between two closures; mutably in one closure. This is an artificial situation, but I find it interesting in the context of learning Rust.

In

Answer 1

Reference counting is unnecessary here because the entity lives longer than any of the closures. You can get away with:

fn something(f: &mut Foo) {
    let f = RefCell::new(f);

    let operation = || f.borrow().get();
    let notify = || {
        f.borrow_mut().incr();
    };

    retry(operation, notify);

    println!("{:?}", f);
}

which is quite simpler.

The use of RefCell, however, is necessary to move the enforcement of the Aliasing XOR Mutability from compile-time to run-time.