Rc

Rc is a reference-counted shared pointer. Use this when you need to refer to the same data from multiple places:

use std::rc::Rc;
fn main() {
    let mut a = Rc::new(10);
    let mut b = a.clone();
    println!("a: {a}");
    println!("b: {b}");
}
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Shared references in Rust disallow mutation by default. If you need to mutate the data inside an Rc, you will need to wrap the data in a type such as Cell or RefCell, in single-threaded cases. See Arc if you are in a multi-threaded context. Arc stands for โ€œAtomically Reference countedโ€. If you need to mutate through Arc use Mutex, RwLock, or one of the Atomic types.

Speaker Notes
  • Like C++โ€™s std::shared_ptr.
  • clone is cheap: creates a pointer to the same allocation and increases the reference count.
  • make_mut actually clones the inner value if necessary (โ€œclone-on-writeโ€) and returns a mutable reference.