Code shared from the Rust Playground

playground.rs

pub enum Shape {
    Square(f64),
    Circle(f64),
    Triangle { base: f64, height: f64 },
}

impl Shape {
    pub fn area(&self) -> f64 {
        match self {
            Shape::Square(side) => side * side,
            Shape::Circle(radius) => std::f64::consts::PI * radius * radius,
            Shape::Triangle { base, height } => 0.5 * base * height,
        }
    }
}

fn main() {
    let square = Shape::Square(4.0);
    let circle = Shape::Circle(3.0);
    let triangle = Shape::Triangle { base: 5.0, height: 2.0 };

    println!("Area of the square: {}", square.area());
    println!("Area of the circle: {}", circle.area());
    println!("Area of the triangle: {}", triangle.area());
}