ent.rs

#[derive(Debug)]
struct Entity {
    x: u16,
    y: u16,
}

impl Entity {
    fn update(&mut self) -> Option<Entity> {
        if self.x == u16::MAX {
            self.x = 0;
        } else {
            self.x += 1;
        }
        if self.y == u16::MAX {
            self.y = 0;
        } else {
            self.y += 1;
        }

        if self.x == 0 || self.y == 0 {
            return Some(self.spawn());
        }

        None
    }

    fn spawn(&self) -> Entity {
        Entity {
            x: self.x + 1,
            y: self.y + 1,
        }
    }
}

fn main() {
    let mut evec = vec![
        Entity { x: 1, y: 1 },
        Entity { x: 2, y: 2 },
        Entity {
            x: u16::MAX - 1,
            y: 3,
        },
    ];

    for _ in 0..10 {
        let mut new_entities_this_frame = Vec::new();

        for i in &mut evec {
            if let Some(e) = i.update() {
                new_entities_this_frame.push(e);
            }
        }

        evec.append(&mut new_entities_this_frame);
    }

    println!("Hello, {:?}!", evec);
}