Method remove_from_list

code/chapter09/lru.rs:115–145

(&mut self, i: usize)

    }

    fn remove_from_list(&mut self, i: usize) {
        let (prev, next) = {
            let entry = self.entries.get_mut(i).unwrap();
            (entry.prev, entry.next)
        };

        match (prev, next) {
            // 数据项在缓存中间
            (Some(j), Some(k)) => {
                let head = &mut self.entries[j];
                head.next = next;
                let next = &mut self.entries[k];
                next.prev = prev;
            },
            // 数据项在缓存末尾
            (Some(j), None) => {
                let head = &mut self.entries[j];
                head.next = None;
                self.tail = prev;
            },
            // 数据项在缓存头部
            _ => {
                if self.len() > 1 {
                    let head = &mut self.entries[0];
                    head.next = None;
                    let next = &mut self.entries[1];
                    next.prev = None;
                }
            },
        }
    }

    // 确保容量足够，满了就移除末尾的元素
    fn ensure_room(&mut self) {