Static vs Dynamic Dispatch (Generics vs dyn Trait)

trait Drawer {
    fn draw(&self);
}

struct Button;
impl Drawer for Button { fn draw(&self) { println!("Drawing Button"); } }

struct Canvas;
impl Drawer for Canvas { fn draw(&self) { println!("Drawing Canvas"); } }

// Dynamic dispatch: Heterogeneous collection using fat pointers
fn render_all(items: &[Box<dyn Drawer>]) {
    for item in items {
        item.draw(); // Looks up fn pointer in VTable at runtime
    }
}

fn main() {
    let widgets: Vec<Box<dyn Drawer>> = vec![
        Box::new(Button),
        Box::new(Canvas),
    ];
    render_all(&widgets);
}