trait Material {}

struct Iron {}

impl Material for Iron {}

struct Sphere<'a> {
    radius: f64,
    material: &'a dyn Material,
}

fn main() {
    let m1 = Box::new(Iron{});
    let s1 = Sphere{ radius: 1.0, material: &*m1 };
    let s2 = Sphere { radius: 2.0, material: &*m1 };
}