Method remove_tail

code/chapter09/lru.rs:154–164

(&mut self)

    }

    fn remove_tail(&mut self) {
        if let Some(index) = self.tail {
            self.remove_from_list(index);
            let key = &self.entries[index].key;
            self.map.remove(key);
        }

        if self.tail.is_none() {
            self.head = None;
        }
    }
}

fn main() {