Repository: ClickHouse/ClickHouse
File: src/Functions/FunctionsStringDistance.cpp (C++)

Code before:
        using Set = HashSet<UInt32, DefaultHash<UInt32>>;
        Set haystack_utf8_set;
        Set needle_utf8_set;
    };

    using ScratchType = std::conditional_t<is_utf8, ScratchUTF8, ScratchASCII>;

    using ResultType = Float64;
    static ResultType process(
        const char * __restrict haystack, size_t haystack_size, const char * __restrict needle, size_t needle_size)
    {
        if (haystack_size == 0 || needle_size == 0)
            return 0;

        const char * haystack_end = haystack + haystack_size;
        const char * needle_end = needle + needle_size;

        ScratchType scratch;

        if constexpr (is_utf8)
        {
            parseUTF8String(
                haystack,
                haystack_size,
                [&](UInt32 data) { scratch.haystack_utf8_set.insert(data); },
                {});
            parseUTF8String(
                needle, needle_size, [&](UInt32 data) { scratch.needle_utf8_set.insert(data); }, {});
        }
        else
        {
            while (haystack < haystack_end)
            {
                scratch.haystack_set[static_cast<unsigned char>(*haystack)] = 1;
                ++haystack;
            }
            while (needle < needle_end)
            {
                scratch.needle_set[static_cast<unsigned char>(*needle)] = 1;
                ++needle;
            }
        }

        using CalcType = typename ScratchType::CalcType;

        CalcType intersection = 0;
        CalcType union_size = 0;

        if constexpr (is_utf8)
        {
            const auto & small = (scratch.haystack_utf8_set.size() < scratch.needle_utf8_set.size()) ? scratch.haystack_utf8_set : scratch.needle_utf8_set;

Review comment (bug):
The empty initializer `{}` as the second argument is unclear. Since `parseUTF8String` expects a `std::function<void(unsigned char)>` for the `ascii_consumer` parameter, passing an empty initializer may not properly convey intent. Consider passing `nullptr` explicitly to make it clear that ASCII handling is intentionally disabled, or ensure that an empty lambda is used if type requirements necessitate it.

Code after:
        Set needle_utf8_set;
    };

    using ScratchType = std::conditional_t<is_utf8, ScratchUTF8, ScratchASCII>;

    using ResultType = Float64;
    static ResultType process(
        const char * __restrict haystack, size_t haystack_size, const char * __restrict needle, size_t needle_size)
    {
        if (haystack_size == 0 || needle_size == 0)
            return 0;

        const char * haystack_end = haystack + haystack_size;
        const char * needle_end = needle + needle_size;

        ScratchType scratch;

        if constexpr (is_utf8)
        {
            parseUTF8String(
                haystack,
                haystack_size,
                [&](UInt32 data) { scratch.haystack_utf8_set.insert(data); });
            parseUTF8String(
                needle, needle_size, [&](UInt32 data) { scratch.needle_utf8_set.insert(data); });
        }
        else
        {
            while (haystack < haystack_end)
            {
                scratch.haystack_set[static_cast<unsigned char>(*haystack)] = 1;
                ++haystack;
            }
            while (needle < needle_end)
            {
                scratch.needle_set[static_cast<unsigned char>(*needle)] = 1;
                ++needle;
            }
        }

        using CalcType = typename ScratchType::CalcType;

        CalcType intersection = 0;
        CalcType union_size = 0;

        if constexpr (is_utf8)
        {
            const auto & small = (scratch.haystack_utf8_set.size() < scratch.needle_utf8_set.size()) ? scratch.haystack_utf8_set : scratch.needle_utf8_set;
            const auto & large = (scratch.haystack_utf8_set.size() < scratch.needle_utf8_set.size()) ? scratch.needle_utf8_set : scratch.haystack_utf8_set;

            for (auto it = small.begin(); it != small.end(); ++it)