pub enum Thing {
    Foo { y: u64 },
    Bar { z: u64 },
}
pub struct Things {
    pub things: Vec<Thing>,
}

impl Things {
    fn tick(&mut self) {
        for thing in self.things.iter_mut() {
            match thing {
                Thing::Foo { y } => {
                    y -= 1;
                },
                Thing::Bar { z } => {
                    z += 1;
                },
            }
        }
    }
}

fn main() {
    let mut things = Things {
        things: Vec::new()
    };
    things.things.push(Thing::Foo { y: 1 });
    things.things.push(Thing::Bar { z: 1 });
    things.tick();
}