Trait bounds in Rust - Mini Project: Build & Apply

Trait bounds

📖 Scenario: You are building a small Rust program that works with different types of shapes. Each shape can calculate its area. You want to write a function that can accept any shape, as long as it can calculate its area.

🎯 Goal: Create a trait called Shape with a method area. Then write a function print_area that accepts any type implementing the Shape trait and prints its area.

📋 What You'll Learn

Create a trait named Shape with a method area that returns an f64.

Create a struct Circle with a field radius of type f64.

Implement the Shape trait for Circle.

Create a function print_area that accepts a generic parameter with a trait bound Shape.

Call print_area with a Circle instance and print the area.

💡 Why This Matters

🌍 Real World

Traits let you write flexible code that works with many types sharing common behavior, like shapes calculating area.

💼 Career

Understanding trait bounds is essential for writing reusable and safe Rust code, a key skill for Rust developers.

1

Create the Circle struct

Create a struct called Circle with one field radius of type f64.

Rust

# Your code here

Hint

Use struct Circle { radius: f64 } to define the shape.

2

Create the Shape trait

Create a trait called Shape with a method area that returns an f64.

Rust

struct Circle {
    radius: f64,
}

# Your code here

Hint

Use trait Shape { fn area(&self) -> f64; } to define the trait.

3

Implement Shape for Circle

Implement the Shape trait for Circle. The area method should return 3.14 * radius * radius.

Rust

struct Circle {
    radius: f64,
}

trait Shape {
    fn area(&self) -> f64;
}

# Your code here

Hint

Use impl Shape for Circle { fn area(&self) -> f64 { 3.14 * self.radius * self.radius } }.

4

Write print_area function and call it

Write a function called print_area that accepts a generic parameter T with a trait bound Shape. Inside, print the area using println!("Area: {}", shape.area()). Then create a Circle with radius 5.0 and call print_area with it.

Rust

struct Circle {
    radius: f64,
}

trait Shape {
    fn area(&self) -> f64;
}

impl Shape for Circle {
    fn area(&self) -> f64 {
        3.14 * self.radius * self.radius
    }
}

# Your code here

Hint

Use fn print_area(shape: &T) and call print_area(&circle) in main.