QtConcurrent::mappedReduced without mapped

Roman.Podymov

I already asked this question here, but there is still no answer.
Consider the following code (Qt 6.0.3, C++17):

const QVector<int> arr = {1, 2, 3, 4, 5};
auto future = QtConcurrent::mappedReduced<int>(arr, [](auto item) {
    return item;
}, [](int& result, auto item) {
    result += item;
});

As you can see the first lambda expression passed to QtConcurrent::mappedReduced looks unnecessary. That's why I want to find something like QtConcurrent::reduced in Qt 6. Or how can I refactor this code to use only 1 lambda expression?

SGaist

Hi and welcome to devnet,

You can use std::accumulate.

The goal of QtConcurrent mappedReduce is the apply an operation on all the items of container in a concurrent fashion and once done do the reduction.

In your case there's nothing to be done but the sum of the items so there's no need for mappedReduce.

Roman.Podymov

Hello @SGaist
Thank you for your message. We can continue here.