Rc<RefCell<T>> in Rust

Shared ownership plus interior mutability: several handles onto one mutable value.

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

fn main() {
    let shared = Rc::new(RefCell::new(vec!["basics".to_string()]));

    let editor = Rc::clone(&shared);
    editor.borrow_mut().push("traits".to_string());

    let viewer = Rc::clone(&shared);
    println!("{:?}", viewer.borrow());
    println!("owners: {}", Rc::strong_count(&shared));

    shared.borrow_mut().retain(|t| t != "basics");
    println!("{:?}", editor.borrow());
}

How it works

1. Rc counts owners; RefCell allows the mutation.
2. Every clone sees the same underlying value.
3. This combination is single-threaded only.

Keywords and builtins used here

• fn
• let
• main
• use

The run, in numbers

Lines

16

Characters to type

404

Tokens

143

Three-star pace

110 tpm

At the three-star pace of 110 tokens a minute, this run takes about 78 seconds.

Type this snippet

Step 2 of 3 in Interior mutability, step 8 of 11 in Lifetimes & interior mutability.

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