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C++17 in Detail: A Deep Dive

More Algorithms

This section introduces two more algorithms, the fused and scan algorithms!

We'll cover the following...

transform_reduce - Fused Algorithm

To get even more flexibility and performance, the reduce algorithm also has a version where you can apply a transform operation before performing the reduction.

C++
int main() {
  std::vector<int> v{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  auto sumTransformed = std::transform_reduce(std::execution::par,
      v.begin(),
      v.end(),
      0,
      std::plus<int>{},
      [](const int& i) { return i * 2; }
  );
  cout << sumTransformed;
  return 0;
}

​The above code will first execute the unary functor - the lambda that doubles the input value; then the results will be reduced into a single sum.

The fused version will be faster than using two algorithms: std::reduce ...