Trait objects overview in Rust - Mini Project: Build & Apply

Trait objects overview

📖 Scenario: Imagine you are building a simple drawing app. You want to store different shapes like circles and rectangles in one list and draw them all.

🎯 Goal: You will create a list of shapes using trait objects so you can call the draw method on each shape without knowing its exact type.

📋 What You'll Learn

Create a trait called Shape with a method draw

Create two structs: Circle and Rectangle

Implement the Shape trait for both structs

Create a vector of Box<dyn Shape> holding different shapes

Use a for loop to call draw on each shape

Print the drawing messages exactly as specified

💡 Why This Matters

🌍 Real World

Trait objects let you write flexible code that works with different types through a common interface. This is useful in graphics apps, game engines, and plugins.

💼 Career

Understanding trait objects is important for Rust developers to write clean, reusable, and extensible code that handles multiple types uniformly.

1

Create the Shape trait and structs

Create a trait called Shape with a method draw(&self) that returns nothing. Then create two structs called Circle and Rectangle with no fields.

Rust

# Your code here

Hint

Traits are like interfaces. Define Shape with fn draw(&self);. Then define empty structs Circle and Rectangle.

2

Implement Shape for Circle and Rectangle

Implement the Shape trait for Circle and Rectangle. For Circle, draw should print "Drawing a circle". For Rectangle, draw should print "Drawing a rectangle".

Rust

trait Shape {
    fn draw(&self);
}

struct Circle;
struct Rectangle;

// Your code here

Hint

Use impl Shape for Circle and define fn draw(&self) to print the message. Do the same for Rectangle.

3

Create a vector of Box<dyn Shape> with shapes

Create a mutable vector called shapes of type Vec<Box<dyn Shape>>. Add a Box::new(Circle) and a Box::new(Rectangle) to the vector.

Rust

trait Shape {
    fn draw(&self);
}

struct Circle;
struct Rectangle;

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

impl Shape for Rectangle {
    fn draw(&self) {
        println!("Drawing a rectangle");
    }
}

// Your code here

Hint

Use Vec<Box<dyn Shape>> to hold different shapes. Add shapes with shapes.push(Box::new(Circle)).

4

Call draw on each shape and print output

Use a for loop with shape to iterate over shapes.iter(). Inside the loop, call shape.draw(). This will print the drawing messages.

Rust

trait Shape {
    fn draw(&self);
}

struct Circle;
struct Rectangle;

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

impl Shape for Rectangle {
    fn draw(&self) {
        println!("Drawing a rectangle");
    }
}

fn main() {
    let mut shapes: Vec> = Vec::new();
    shapes.push(Box::new(Circle));
    shapes.push(Box::new(Rectangle));

    // Your code here
}

Hint

Use for shape in shapes.iter() and call shape.draw() inside the loop to print the messages.