QtConcurrent::map and class member

yoavmil

I want to use QtConcurrent::map on a class member, but it doesn't complie. where as there is a way to use QtConcurrent::run on a class member: QtConcurrent::run(pointer, method, argument ...).
as a workaround, I used a non-method-function that calls the method function through a static pointer (this will work only on a singlton class, which is my case).
please advise.

Chris Kawa

Assuming MyClass::doIt() is the method you want to call, if you're on a c++11 compiler a simple lambda will do:

void MyClass::foo() {
    QList<int> list {1,2,3,4};
    auto future = QtConcurrent::map(list, [&](int i){ doIt(i); }); //"this" captured implicitly
    future.waitForFinished();
}

If not then you can use a lambda-like local struct:

void MyClass::foo() {
    QList<int> list; //no initializer list in c++98 :(
    list << 1 << 2 << 3 << 4;

    struct Lambdish {
        MyClass* m_;
        Lambdish(MyClass* m) :m_(m) {}
        void operator()(int i) { m_->doIt(i); }
    } lambdish(this);

    QFuture<void>future = QtConcurrent::map(list, lambdish); //no auto or lambdas in c++98 :(
    future.waitForFinished();
}

Oh, and just remember that if the parameter is anything but simple type (int, float etc.) the lambda and the lambdish operator() should take it by reference.

yoavmil

thanks Chris. this is ok. however, I just want to point out the the QtConccurent API is missing the QtConcurrent::map overload that gets a pointer and a method, like QtConcurrent::run has.

JKSH

@yoavmil said:

I just want to point out the the QtConccurent API is missing the QtConcurrent::map overload that gets a pointer and a method, like QtConcurrent::run has.

Do you mean this?: http://doc.qt.io/qt-5/qtconcurrentmap.html#using-member-functions