What are trait objects in Rust

Type System
2026-04-17T12:05:42+00:00
Trait objects let you store different types in a collection by focusing on shared behavior defined by a trait.

Trait objects in Rust allow you to store values of different types in a collection as long as they all implement a specific trait, enabling dynamic dispatch. You create them by boxing the trait object or using a reference to it, which lets the compiler call the correct method at runtime based on the actual type.

trait Draw {
    fn draw(&self);
}

struct Circle;
struct Square;

impl Draw for Circle {
    fn draw(&self) { println!("Drawing circle"); }
}

impl Draw for Square {
    fn draw(&self) { println!("Drawing square"); }
}

fn main() {
    let c = Box::new(Circle);
    let s = Box::new(Square);
    let shapes: Vec<Box<dyn Draw>> = vec![c, s];
    for shape in shapes {
        shape.draw();
    }
}