struct A;
struct B;

trait Walk {
    fn walk(&self);
}

impl Walk for A {
    fn walk(&self) {
        println!("A walks");
    }
}

impl Walk for B {
    fn walk(&self) {
        println!("B walks");
    }
}

fn main() {
    let random = 42; // chosen randomly
    let person: Box<Walk> = if random > 39 { Box::new(A{}) } else { Box::new(B{}) };
    person.walk();
}