Mastering Rust - Second Edition

Reference counted smart pointers

The ownership rule allows only one owner to exist at a time in a given scope. However, there are cases where you need to share the type with multiple variables. For instance, in a GUI library, each of the child widgets needs to have a reference to its parent container widget for things like communicating to layout the child widget based on resize events from the user. While lifetimes allow you to reference the parent node from the child nodes by storing the parent as a &'a Parent (say), it's often limited by the lifetime 'a of the value. Once the scope ends, your reference is invalid. In such cases, we need more flexible approaches, and that calls for using reference counting types. These smart pointer types ...