Rc<T>, Box<T>, RefCell<T>, Cell<T>

https://doc.rust-lang.org/book/ch15-05-interior-mutability.html#enforcing-borrowing-rules-at-runtime-with-refcellt

• Rc enables multiple owners of the same data; Box and RefCell have single owners.
• Box allows immutable or mutable borrows checked at compile time; Rc allows only immutable borrows checked at compile time; RefCell allows immutable or mutable borrows checked at runtime.
• Because RefCell allows mutable borrows checked at runtime, you can mutate the value inside the RefCell even when the RefCell is immutable.

The standard library has other types that provide interior mutability, such as Cell, which is similar except that instead of giving references to the inner value, the value is copied in and out of the Cell. There’s also Mutex, which offers interior mutability that’s safe to use across threads