Shared via Rust Playground

playground.rs

struct Thing {
    pub num: i32,
}

impl Thing {
    pub fn new(n: i32) -> Thing {
        Thing { num: n }
    }

    pub fn add_total(&mut self, things: &ThingContainer) {
        self.num += things.sum_all();
    }
}

struct ThingContainer {
    thing1: Thing,
    thing2: Thing,
}

impl ThingContainer {
    pub fn new() -> ThingContainer {
        ThingContainer {
            thing1: Thing::new(5),
            thing2: Thing::new(2),
        }
    }

    pub fn sum_all(&self) -> i32 {
        self.thing1.num + self.thing2.num
    }

    pub fn do_stuff(&mut self) {
        self.thing1.add_total(self);
    }
}

fn main() {
    let mut things = ThingContainer::new();
    things.do_stuff();
    assert!(things.sum_all() == (5 + (5 + 2)) + 2)
}