implement common methods with global function or polymorphism

global-function.rs

struct Example {
    number: i32,
}
impl Example {
    fn boo() {
        println!("boo! Example::boo() was called!");
    }
    fn answer(&mut self) {
        self.number += 42;
    }
    fn get_number(&self) -> i32 {
        self.number
    }
}
trait Thingy {
    fn do_thingy(&self) {
        println!("doing a thing! also, number is {}!", self.number);
    }
}
impl Thingy for Example {}
// main
fn main() {
    let e = Example { number: 99 };
    e.do_thingy();
}

polymorphism.rs

struct Super {}
trait SuperTrait<T: Staff> {
    fn common_method(common: T);
}
impl<T: Staff> SuperTrait<T> for Super {
    fn common_method(state: T) {
        println!("get number via super: {}.", state.get_number());
    }
}
struct X {
    width: i32,
}
struct Y {
    height: i32,
}
trait Staff {
    fn get_number(&self) -> i32;
}
impl Staff for X {
    fn get_number(&self) -> i32 {
        self.width
    }
}
impl Staff for Y {
    fn get_number(&self) -> i32 {
        self.height
    }
}
fn main() {
    let x = X { width: 1 };
    let y = Y { height: 2 };
    Super::common_method(x);
    Super::common_method(y);
}