% Trait Objects
There is a new edition of the book and this is an old link.
Trait objects combine the data made up of the pointer to a concrete object with the behavior of the methods defined in the trait. A trait defines behavior that we need in a given situation. We can then use a trait as a trait object in places where we would use a concrete type or a generic type.
pub struct InputBox { pub label: String, } impl Draw for InputBox { fn draw(&self) { // Code to actually draw an input box } } pub struct Button { pub label: String, } impl Draw for Button { fn draw(&self) { // Code to actually draw a button } } pub struct Screen<T: Draw> { pub components: Vec<T>, } impl<T> Screen<T> where T: Draw { pub fn run(&self) { for component in self.components.iter() { component.draw(); } } } fn main() { let screen = Screen { components: vec![ Box::new(InputBox { label: String::from("OK"), }), Box::new(Button { label: String::from("OK"), }), ], }; screen.run(); }
Here are the relevant sections in the new and old books: