There is a new edition of the book and this is an old link.
Drop
lets us customize what happens when a value is about to go out of scope.
struct CustomSmartPointer { data: String, } impl Drop for CustomSmartPointer { fn drop(&mut self) { println!("Dropping CustomSmartPointer with data `{}`!", self.data); } } fn main() { let c = CustomSmartPointer { data: String::from("my stuff") }; let d = CustomSmartPointer { data: String::from("other stuff") }; println!("CustomSmartPointers created."); }Run
Here are the relevant sections in the new and old books: