captainurist

class StringFormatState {
public:
    using value_type = wchar_t;

    StringFormatState() : m_debug(&m_result) {
        m_debug = m_debug.nospace();
    }

    void append(wchar_t character) {
        /* Surrogates are not supported. */

captainurist

template<class T>
concept debug_streamable = requires (QDebug a, T b) { a << b; };

template<class T> requires debug_streamable<T> && std::is_class_v<std::remove_cvref_t<T>>
struct std::formatter<T, wchar_t> : public formatter<QStringView, wchar_t> {
    using base_type = formatter<QStringView, wchar_t>;

    template <typename FormatContext>
    auto format(const T& value, FormatContext& ctx) {
        QString buffer;

captainurist

template<>
struct std::formatter<QStringView, wchar_t> : public formatter<std::wstring_view, wchar_t> {
    using base_type = formatter<std::wstring_view, wchar_t>;

    template <class FormatContext>
    auto format(QStringView value, FormatContext& ctx) {
        QStringToWcharConversionBuffer buffer(value);
        return base_type::format(buffer.view(), ctx);
    }
};

captainurist

class QStringToWcharConversionBuffer {
public:
    QStringToWcharConversionBuffer(QStringView source) {
        if (sizeof(wchar_t) == sizeof(QChar)) {
            const wchar_t* data = reinterpret_cast<const wchar_t*>(source.data());
            m_view = std::wstring_view(data, data + source.size());
        } else {
            m_buffer.reserve(source.size());
            qsizetype size = source.toWCharArray(m_buffer.data());
            m_view = std::wstring_view(m_buffer.data(), size);

captainurist

template<class... Args>
QString sformat(std::wstring_view formatString, Args&&... args) {
    QString result;
    QStringBackInsertConvertingProxy resultProxy(&result);
    std::format_to(std::back_inserter(resultProxy), formatString, std::forward<Args>(args)...);
    return result;
}

// Then this works:
QString s = sformat(L"X = {:#x}", 123);

captainurist

struct QStringBackInsertConvertingProxy {
public:
    using value_type = wchar_t;

    QStringBackInsertConvertingProxy(QString* target) : m_target(target) {}

    void push_back(wchar_t character) {
        /* Surrogates are not supported. */
        assert(sizeof(wchar_t) == sizeof(char16_t) || !QChar::requiresSurrogates(static_cast<char32_t>(character)));

captainurist

return BadCastException::tr("Could not deserialize value '%1' as %3").arg("x").arg("int");

captainurist

return BadCastException::tr("Could not deserialize value '%1' as %2").arg("x").arg("int");