QtConcurrency::mapped with a member function

Question

How can I use QtConcurrent::mapped with a member function as operator? Currently I'm using a callable object (which is ugly solution):

struct Vectorizer {
    Vectorizer(DialogCreateSamples* cs)
    : m_createSamples(cs) { }

    typedef QString result_type;

    QString operator()(const QString &input)
    {
        return m_createSamples->generateVector(input);
    }

    DialogCreateSamples* m_createSamples;
};
QFuture<QString> future = QtConcurrent::mapped(m_inputs,Vectorizer(this));

Also tried to pass lambda expressions but compiler says there is no result_type defined in lambda. This works with QtConcurrent::map because map do not need result_type. So if I can add a typedef in lambda it should work...

Answer 1

Maybe bind? Either std::bind if you're using C++11 or std::tr1::bind or boost::bind otherwise.

Something like:

QtConcurrent::mapped(m_inputs, std::bind(&Class::member_function, pointerToObjectOfTypeClass /* this? */, _1 /* placeholder for argument of your function filled by data from m_inputs */));

We use this in our code; example at: https://github.com/clementine-player/Clementine/blob/d03c1aa2419a0ceefd7f65114c1ac8991790b716/src/playlist/playlistbackend.cpp#L187

Hope it helps.