Definition #![allow(unused)] fn main() { pub trait Summary { fn summarize(&self) -> String; } } Implementation #![allow(unused)] fn main() { pub trait Summary { fn summarize(&self) -> String; } pub struct NewsArticle { pub headline: String, pub location: String, pub author: String, pub content: String, } impl Summary for NewsArticle { fn summarize(&self) -> String { format!("{}, by {} ({})", self.headline, self.author, self.location) } } pub struct Tweet { pub username: String, pub content: String, pub reply: bool, pub retweet: bool, } impl Summary for Tweet { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } } } Default Implementations #![allow(unused)] fn main() { pub trait Summary { fn summarize(&self) -> String { String::from("(Read more...)") } } pub struct NewsArticle { pub headline: String, pub location: String, pub author: String, pub content: String, } impl Summary for NewsArticle {} pub struct Tweet { pub username: String, pub content: String, pub reply: bool, pub retweet: bool, } impl Summary for Tweet { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } } } Traits as Parameters pub trait Summary { fn summarize(&self) -> String; } pub struct NewsArticle { pub headline: String, pub location: String, pub author: String, pub content: String, } impl Summary for NewsArticle { fn summarize(&self) -> String { format!("{}, by {} ({})", self.headline, self.author, self.location) } } pub struct Tweet { pub username: String, pub content: String, pub reply: bool, pub retweet: bool, } impl Summary for Tweet { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } } pub fn notify(item: &impl Summary) { println!("Breaking news! {}", item.summarize()); } Specifying Multiple Trait Bounds pub fn notify(item: &(impl Summary + Display)) { This also works on generic types: pub fn notify<T: Summary + Display>(item: &T) { Clearer Trait Bounds fn some_function<T: Display + Clone, U: Clone + Debug>(t: &T, u: &U) -> i32 { is the same as fn some_function<T, U>(t: &T, u: &U) -> i32 where T: Display + Clone, U: Clone + Debug { Return Types that Implement Traits pub trait Summary { fn summarize(&self) -> String; } pub struct NewsArticle { pub headline: String, pub location: String, pub author: String, pub content: String, } impl Summary for NewsArticle { fn summarize(&self) -> String { format!("{}, by {} ({})", self.headline, self.author, self.location) } } pub struct Tweet { pub username: String, pub content: String, pub reply: bool, pub retweet: bool, } impl Summary for Tweet { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } } fn returns_summarizable() -> impl Summary { Tweet { username: String::from("horse_ebooks"), content: String::from( "of course, as you probably already know, people", ), reply: false, retweet: false, } }