Rust — Traits

Basic trait

trait Summary {
    fn summarize(&self) -> String;
}

struct Article {
    title: String,
    content: String,
}

impl Summary for Article {
    fn summarize(&self) -> String {
        format!("{}: {}", self.title, &self.content[..50])
    }
}

Default implementations

trait Summary {
    fn summarize(&self) -> String;

    fn preview(&self) -> String {
        format!("{}...", &self.summarize()[..20])
    }
}

Traits as parameters

fn notify(item: &impl Summary) {
    println!("Breaking: {}", item.summarize());
}

// Trait bound syntax
fn notify2<T: Summary>(item: &T) {
    println!("Breaking: {}", item.summarize());
}

// Multiple traits
fn display(item: &(impl Summary + std::fmt::Display)) {
    println!("{}", item);
}

Return traits

fn create_summarizable() -> impl Summary {
    Article {
        title: String::from("News"),
        content: String::from("Something important happened today..."),
    }
}

Trait bounds

use std::fmt::Display;

fn longest_with_announcement<'a, T: Display>(
    x: &'a str,
    y: &'a str,
    ann: T,
) -> &'a str {
    println!("Announcement: {}", ann);
    if x.len() > y.len() { x } else { y }
}

Derive traits

#[derive(Debug, Clone, PartialEq)]
struct Point {
    x: f64,
    y: f64,
}

fn main() {
    let p1 = Point { x: 1.0, y: 2.0 };
    let p2 = p1.clone();
    println!("{:?}", p1);
    println!("Equal: {}", p1 == p2);
}

Mini Practice

Write Rust code that:

1. Defines a trait with a method
2. Implements the trait for a struct
3. Uses trait bounds in a function
4. Derives common traits

Up Next

In the next lesson, you'll learn about Generics — writing reusable code.