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% Trait Objects
<small>There is a new edition of the book and this is an old link.</small>
> 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.
```rust,ignore
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:
* **[in the current edition: Ch 17.02 — Trait Objects][2]**
* <small>[In the first edition: Ch 3.22 — Trait Objects][1]</small>
[1]: https://doc.rust-lang.org/1.30.0/book/first-edition/trait-objects.html
[2]: ch17-02-trait-objects.html
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