Question

I have a QList and want to process all its elements in parallel. The problem is I need to pass an argument to my_function. The code below doesn’t allow for this.

QList<something> output = QtConcurrent::blockingMapped(
    input,
    my_function
);

I may use a distinct function for each set of parameters. I may use a global variable too. I may try to rewrite the build in QT function too. However, there should be a better solution. Any idea?

Answer 1

Assuming that the argument you want to pass to the function is independent of the items, you can create a functor that extends std::unary_function<const something&,void> whose constructor takes the argument you want to pass to it. Then, use the functor where you would use the function. E.g.,

struct MyFunctor : public std::unary_function<const something&,void> {
public:
  myFunctor(int s) { _i = i; }
  void operator()(something& str) {
    something.apply(_i);
  }
private:
  int _i;
};

…

MyFunctor myFunctor(i);
QList<something> output = QtConcurrent::blockingMapped(
    input,
    myFunctor
);