C++中文周刊周末圆桌讨论 1118

## 周刊内容鉴赏之UB鉴赏 栈溢出
                        ```C++
                        struct Node {
                            int value = 0;
                            std::vector<Node> childrens;
                        };
                        
                        struct List {
                            int value = 0;
                            std::unique_ptr<List> next;
                        
                            ~List() {
                                while (next) {
                                    // The destructor is still recursive,
                                    // but now the recursion depth is 1 call.
                                    next = std::move(next->next);
                                }
                            }
                        
                            List() noexcept = default;
                            List(List&&) noexcept = default;
                            List& operator=(List&&) noexcept = default;
                        };
                        ```

## 常规设计
                        ```txt
                        * Short strings, length <= 12
                        | Bytes 0-3  | Bytes 4-15                            |
                        |------------|---------------------------------------|
                        | length     | data (padded with 0)                  |

* Long strings, length > 12
                        | Bytes 0-3  | Bytes 4-7  | Bytes 8-15 |
                        |------------|------------|------------|
                        | length     | prefix     |  ptr     |
                        ```
                        符合使用直觉

```c++
                        bool isEqual(data128_t a, data128_t b) {
                            if (a.v[0] != b.v[0]) return false;
                            auto len = (uint32_t) a.v[0];
                            if (len <= 12) return a.v[1] == b.v[1];
                            return memcmp((char*) a.v[1], (char*) b.v[1], len) == 0;
                        }
                        ```

## 代码鉴赏环节
                        - https://github.com/apache/kvrocks/pull/2648
                        ```diff
                         is_txn_mode_ = true;
                        - txn_write_batch_ =
                        -    std::make_unique<rocksdb::WriteBatchWithIndex>(rocksdb::BytewiseComparator() /*default backup_index_comparator */,
                        -                                                   0 /* default reserved_bytes*/, GetWriteBatchMaxBytes());
                        + // Set overwrite_key to false to avoid overwriting the existing key in case
                        + // like downstream would parse the replication log etc.
                        + txn_write_batch_ = std::make_unique<rocksdb::WriteBatchWithIndex>(
                        +    /*backup_index_comparator=*/rocksdb::BytewiseComparator(),
                        +    /*reserved_bytes=*/0, /*overwrite_key=*/false, /*max_bytes=*/GetWriteBatchMaxBytes());
                        + return Status::OK();
  
                        ```
                        ```C++
                        explicit WriteBatchWithIndex(
                            const Comparator* backup_index_comparator = BytewiseComparator(),
                            size_t reserved_bytes = 0, bool overwrite_key = false,
                            size_t max_bytes = 0, size_t protection_bytes_per_key = 0);
                        ```