Structs, enums and traits

use std::fmt;

#[derive(Debug)]
struct Rect {
    width: f64,
    height: f64,
}

enum Shape {
    Rect(Rect),
    Circle { radius: f64 },
}

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

impl Area for Shape {
    fn area(&self) -> f64 {
        match self {
            Shape::Rect(r) => r.width * r.height,
            Shape::Circle { radius } => std::f64::consts::PI * radius * radius,
        }
    }
}

impl Rect {
    fn square(side: f64) -> Self {
        Rect { width: side, height: side }
    }

    fn scale(&mut self, factor: f64) {
        self.width *= factor;
        self.height *= factor;
    }
}

impl fmt::Display for Rect {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Rect({}x{})", self.width, self.height)
    }
}

fn main() {
    let mut r = Rect { width: 3.0, height: 4.0 };
    r.scale(2.0);
    println!("{r} {:?}", Rect::square(1.0));
    let shapes = vec![Shape::Rect(r), Shape::Circle { radius: 1.0 }];
    for s in &shapes {
        println!("{:.2}", s.area());
    }
}