Interior Mutability Concepts

Rc and RefCell

Shared Mutable State

Rc<RefCell<T>> combines shared ownership with checked interior mutation in single-threaded code.

Program

Play the program to choose an increment, clone a shared owner, and update the value through the clone.

shared_refcell.rs 
use std::cell::RefCell;
use std::rc::Rc;

fn main() {
    let delta = ;
    let shared = Rc::new(RefCell::new(10));
    let owner = Rc::clone(&shared);
    *owner.borrow_mut() += delta;
    let value = *shared.borrow();
    println!("{value}");
}

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

fn main() {
    let delta = ;
    let shared = Rc::new(RefCell::new(10));
    let owner = Rc::clone(&shared);
    *owner.borrow_mut() += delta;
    let value = *shared.borrow();
    println!("{value}");
}

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

fn main() {
    let delta = ;
    let shared = Rc::new(RefCell::new(10));
    let owner = Rc::clone(&shared);
    *owner.borrow_mut() += delta;
    let value = *shared.borrow();
    println!("{value}");
}
Rc<RefCell<T>> `Rc` shares ownership, while `RefCell` allows checked mutation of the inner value.
clone handle `Rc::clone` creates another owner of the same allocation.
mutable borrow `borrow_mut` temporarily opens the inner value for mutation.