Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

use std::fmt;

// Trait definition with a required method and a default method
trait Animal {
    fn name(&self) -> &str;
    fn sound(&self) -> &str;

// Default implementation — can be overridden
    fn describe(&self) -> String {
        format!("{} says '{}'", self.name(), self.sound())
    }
}

struct Dog { name: String }
struct Cat { name: String }

impl Animal for Dog {
    fn name(&self) -> &str { &self.name }
    fn sound(&self) -> &str { "woof" }
    // Uses default describe()
}

impl Animal for Cat {
    fn name(&self) -> &str { &self.name }
    fn sound(&self) -> &str { "meow" }

// Override the default
    fn describe(&self) -> String {
        format!("{} says '{}' and ignores you", self.name(), self.sound())
    }
}

// Display is a standard-library trait
impl fmt::Display for Dog {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "Dog({})", self.name)
    }
}

fn print_animal(a: &dyn Animal) {
    println!("{}", a.describe());
}

fn main() {
    let dog = Dog { name: "Rex".to_string() };
    let cat = Cat { name: "Whiskers".to_string() };

print_animal(&dog);
    print_animal(&cat);
    println!("{dog}");  // uses Display impl

// Trait objects in a Vec
    let animals: Vec<Box<dyn Animal>> = vec![
        Box::new(Dog { name: "Buddy".to_string() }),
        Box::new(Cat { name: "Luna".to_string() }),
    ];
    for a in &animals {
        println!("{}", a.describe());
    }
}