Trying to use a trait as a field in an enum

trait_in_enum.rs

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

struct Circle {
    radius: f32,
}

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

struct Rectangle {
    width: f32,
    height: f32,
}

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

enum Thing {
    Shape(Polygon),
    Point,
}

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

fn main() {
    exec(Thing::Shape(Circle{radius: 5.0}));
    exec(Thing::Shape(Rectangle{width: 7.0, height: 14.0}));
    exec(Thing::Point);
}