Stage 9.15: Combining Smart Pointers

Smart pointers might seem limited, but they can make some very powerful combinations.

Rc<Vec<Foo>> - Allow the cloning of multiple smart pointers that can borrow the same vector of immutable data structures on the heap.

Rc<RefCell<Foo>> - Allow multiple smart pointers the ability to borrow mutably/immutably the same struct Foo

Arc<Mutex<Foo>> - Allow multiple smart pointers the ability to lock temporary mutable/immutable borrows in a CPU thread exclusive manner.

Memory details:

• You'll notice a theme with many of these combinations. The use of a immutable data type (possibly owned by multiple smart pointers) to modify internal data. This is referred to as the "interior mutability" pattern in Rust. It is a pattern that lets us bend the rules of memory usage at runtime with the same level of safety as Rust's compile-time checks.