Function ModifyStringSymbolwise

util/charset/wide.cpp:198–217

template <class TStringType, typename F>
static bool ModifyStringSymbolwise(TStringType& text, size_t pos, size_t count, F&& f) {
    // TODO(yazevnul): this is done for consistency with `TUtf16String::to_lower` and friends
    // at r2914050, maybe worth replacing them with asserts. Also see the same code in `ToTitle`.
    pos = pos < text.size() ? pos : text.size();
    count = count < text.size() - pos ? count : text.size() - pos;

    // TUtf16String is refcounted and it's `data` method return pointer to the constant memory.
    // To simplify the code we do a `const_cast`, though first write to the memory will be done only
    // after we call `Detach()` and get pointer to a writable piece of memory.
    auto* p = const_cast<typename TStringType::value_type*>(text.data() + pos);
    const auto* pe = text.data() + pos + count;

    if (ModifySequence<true>(p, pe, f)) {
        DetachAndFixPointers(text, p, pe);
        ModifySequence<false>(p, pe, f);
        return true;
    }

    return false;
}

bool ToLower(TUtf16String& text, size_t pos, size_t count) {
    const auto f = [](const wchar32 s) { return ToLower(s); };