Method get_mut

publication/code/chapter10/lru.rs:101–110

(&mut self, key: &K)

    }

    fn get_mut(&mut self, key: &K) -> Option<&mut V> {
        if self.contains(key) {
            self.access(key);
        }

        let entries = &mut self.entries;
        self.map.get(key).and_then(move |&i| {
            entries[i].val.as_mut()
        })
    }

    fn contains(&mut self, key: &K) -> bool {
        self.map.contains_key(key)