Trying to use a trait as a field in an enum

trait_in_enum_with_box_and_refs.rs

trait Polygon {
    fn area(&self) -> f32;
}

struct Circle<'a> {
    radius: &'a f32,
}

impl<'a> Polygon for Circle<'a> {
    fn area(&self) -> f32 {
        self.radius * std::f32::consts::PI * 2.0
    }
}

struct Rectangle<'a> {
    width: &'a f32,
    height: &'a f32,
}

impl<'a> Polygon for Rectangle<'a> {
    fn area(&self) -> f32 {
        self.width * self.height
    }
}

enum Thing {
    Shape(Box<Polygon>),
    Point,
}

fn exec(t: Thing) {
    match t {
        Thing::Shape(p) => println!("Polygon with area: {}", p.area()),
        Thing::Point => println!("Point"),
    }
}

fn do_stuff(nums: &[f32]) {
    exec(Thing::Shape(Box::new(Circle{radius: &nums[0]})));
    exec(Thing::Shape(Box::new(Rectangle{width: &nums[1], height: &nums[2]})));
    exec(Thing::Point);
}

fn main() {
    let nums = vec![5.0, 7.0, 14.0];
    do_stuff(&nums);
}