pub trait InsertImmutable<Item: Eq + std::hash::Hash> {    fn insert(&self, item: Item) -> bool;} mod trait_impls {    use std::{cell::RefCell, collections::HashSet, hash::Hash};     use dashmap::DashSet;     use super::InsertImmutable;    use crate::cache;     impl<T: Eq + Hash> InsertImmutable<T> for DashSet<T, cache::object::State> {        fn insert(&self, item: T) -> bool {            self.insert(item)        }    }     impl<T: Eq + Hash> InsertImmutable<T> for RefCell<HashSet<T, cache::object::State>> {        fn insert(&self, item: T) -> bool {            self.borrow_mut().insert(item)        }    }} pub struct Chunks<I> {    pub size: usize,    pub iter: I,} impl<I, Item> Iterator for Chunks<I>where    I: Iterator<Item = Item>,{    type Item = Vec<Item>;     fn next(&mut self) -> Option<Self::Item> {        let mut res = Vec::with_capacity(self.size);        let mut items_left = self.size;        for item in &mut self.iter {            res.push(item);            items_left -= 1;            if items_left == 0 {                break;            }        }        (!res.is_empty()).then(|| res)    }}