[Interest] Set manipulation in Qt 6

[André Pönitz]

On Sat, Jun 20, 2020 at 08:44:19AM +0200, Vadim Peretokin wrote:
>    Being good users open-source of Qt, [1]we're looking into our
>    compatibility early on to help report any issues and we're finding this
>    compatibility code to be rather problematic from the developer
>    experience point of view:
>    QMap<QString, QList<QPointF>> customLines;
>    QMap<QString, QColor> customLinesColor;
>    // ...
>    #if (QT_VERSION >= QT_VERSION_CHECK(5, 14, 0))
>        auto customLineKeys = customLines.keys();
>        QSet<QString> missingKeys{customLineKeys.begin(),
>    customLineKeys.end()};
>        if (!customLinesColor.isEmpty()) {
>            auto customLinesColorKeys = customLinesColor.keys();
>            QSet<QString>
>    customLinesColorKeysSet{customLinesColorKeys.begin(),
>    customLinesColorKeys.end()};
>            missingKeys.subtract(customLinesColorKeysSet);
>        }
>    #else
>        QSet<QString>
>    missingKeys{customLines.keys().toSet().subtract(customLinesColor.keys()
>    .toSet())};
>    #endif
>    Are we doing it wrong or is this a regression in Qt? ([2]QTBUG-83697)

I don't think you are doing anything wrong here.

The Qt Creator code base currently has the following in a central header:

    // Replacement for deprecated Qt functionality

    #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    template <class T>
    QSet<T> toSet(const QList<T> &list)
    {
    #if (QT_VERSION < QT_VERSION_CHECK(5, 14, 0))
        return list.toSet();
    #else
        return QSet<T>(list.begin(), list.end());
    #endif
    }
    #endif

    template<class T>
    QSet<T> toSet(const QVector<T> &vec)
    {
    #if (QT_VERSION < QT_VERSION_CHECK(5, 14, 0))
        QSet<T> result;
        for (const T &p : vec) {
            result.insert(p);
        }
        return result;
    #else
        return QSet<T>(vec.begin(), vec.end());
    #endif
    }

    template<class T>
    QList<T> toList(const QSet<T> &set)
    {
    #if (QT_VERSION < QT_VERSION_CHECK(5, 14, 0))
        return set.toList();
    #else
        return QList<T>(set.begin(), set.end());
    #endif
    }

    template <class Key, class T>
    void addToHash(QHash<Key, T> *result, const QHash<Key, T> &additionalContents)
    {
    #if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
        result->unite(additionalContents);
    #else
        result->insert(additionalContents);
    #endif
    }

and used those functions to replace the previously used member functions.

This is not really nice either, but at least keeps the main application code
free of preprocessor #if's.

Andre'




Andre'