typeclass.rs

use std::f64::consts::PI;
trait Shape { fn new(area: f64) -> Self; }
struct Circle { radius: f64 }
struct Square { length: f64 }

impl Shape for Circle {
    fn new(area: f64) -> Circle { Circle { radius: (area / PI).sqrt() } }
}
impl Shape for Square {
    fn new(area: f64) -> Square { Square { length: area.sqrt() } }
}

fn draw_all(shapes: &[Box<Drawable>]) {
    for shape in shapes.iter() { shape.draw(); }
}
trait Drawable { fn draw(&self); }

impl Drawable for Circle { fn draw(&self) { println!("Cirlce {}",self.radius) } }
impl Drawable for Square { fn draw(&self) { println!("Square {}",self.length) } }

fn main() {
  let area = 42.5;
  let c: Box<Circle> = box Shape::new(area);
  let s: Box<Square> = box Shape::new(area);
  draw_all([c,s]);
}