trait OneAdder {
    fn add_one(&mut self);
}

trait AnyAdder {
    fn add_any(&mut self, extra: u32);
}

impl<T:OneAdder> AnyAdder for T  {
    fn add_any(&mut self, value: u32) {
        for _ in 0..value {
            self.add_one()
        }
    }
}

// ---------

#[derive(Debug)]
struct A {
  value: i32,
}

// Let's just implement OneAdder and get AnyAdder for free.
impl OneAdder for A {
    fn add_one(&mut self) {
        self.value += 1;
    }
}

fn main() {
    let mut a = A { value: 5 };
    a.add_any(10);
    println!("{:?}", a)
}