How to flip a static QMap to another static QMap in C++ Qt 6?

Question

I need to map a set of string values to an enum type and back.

In my header file I have:

const static QMap<aMessage::Type, QString> type2str;
const static QMap<QString, aMessage::Type> str2type;

And in the corresponding source file type2str gets initialized OOL with an init-list:

const static QMap<aMessage::Type, QString> type2str
{
    {aMessage::Type::Connect, "connect"},
    {aMessage::Type::Message, "message"},
    {aMessage::Type::Name, "name"},
    {aMessage::Type::Disconnect, "disconnect"},
};

How should I initialize the inverse of type2str into str2type without copy-paste?

Answer 1

If you want to have 2 QMaps Enum->String and String->Enum, you can simply initialize the second map by iterating over the first one:

const static QMap<QString, MsgType> str2type = []() {
    QMap<QString, aMessage::Type> result;
    for (auto it = type2str.keyValueBegin(); it != type2str.keyValueEnd(); ++it) {
        result[it->second] = it->first;
    }
    return result;
}();

Note however that all the keys and values are copied from first map to the other map. If you want to avoid making copies and have a single container, you could use e.g. boost bimap that allows you to do the lookup using first or second element of the map. The example with English<->Spanish dictionary seems to be exactly your case.