Registry.rs

#[derive(Default)]
pub struct Registry {
    counter: usize,
    free: Vec<usize>,
    reclaimed: Vec<usize>,
    reclaimable: bool,
}

impl Registry {
    pub fn new() -> Registry {
        Registry {
            counter: 1,
            free: vec![],
            reclaimed: vec![],
            reclaimable: true,
        }
    }

    pub fn no_reclaim(&mut self) {
        self.reclaim();
        self.reclaimable = false;
    }

    pub fn get_id(&mut self) -> usize {
        match self.free.pop() {
            Some(num) => num,
            None => {
                self.counter += 1;
                self.counter - 1
            }
        }
    }

    pub fn return_id(&mut self, id: usize) {
        if self.reclaimable {
            self.reclaimed.push(id);
        } else {
            self.free.push(id);
        }
    }

    pub fn reclaim(&mut self) {
        self.free.append(&mut self.reclaimed);
    }
}