Method mutate

src/models/common.rs:541–553

(&self, k: K, f: F)

    }

    pub fn mutate<F>(&self, k: K, f: F)
    where
        F: FnOnce(Option<V>) -> Option<V>,
        V: Clone,
    {
        let index = self.hash_key(&k);
        let mut ht = self.hash_table_list[index].lock().unwrap();
        let v = ht.remove(&k);
        let new_v = f(v);
        if let Some(new_v) = new_v {
            ht.insert(k, new_v);
        }
    }

    pub fn get_or_create<F>(&self, k: K, f: F) -> V
    where