[[外部トレイト]]の[[Displayトレイト]]は、[[内部の型]] `User` に実装できる。
```rust
use std::fmt::{Display, Formatter};
struct User {
id: i32,
name: String,
}
impl Display for User {
fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
write!(f, "id: {}, name: {}", self.id, self.name)
}
}
fn main() {
let user = User {
id: 1,
name: String::from("Ichiro"),
};
println!("{}", user);
}
```
```console
$ cargo run
id: 1, name: Ichiro
```