lfu_get_evict

lfu_get_evict.rs

    // return a ref of the most-recently-used entry
    pub fn get(&mut self, key: &'a str) -> Option<&T> where T: Debug{
        self.update_freq_node(key);
        self.by_key.get(key).map(|e| &e.val)
    }

    // evict the least freq used
    fn evict(&mut self) {
        let least_freq_node = self.freq_node.get_mut(&self.least_freq_node).unwrap();
        let least_freq_entry= least_freq_node.pop_front().unwrap();
        self.by_key.remove(least_freq_entry);
    }