std::function versus template argument

function-template-argument.cpp

// Related to https://github.com/InsightSoftwareConsortium/ITK/pull/4347
// PERF: Replace `std::function` with template argument MultiThreaderBase ParallelizeImageRegion, ParallelizeImageRegionRestrictDirection
// Niels Dekker, LKEB, Leiden University Medical Center, 2023

#include <itkImageRegion.h>

#include <algorithm>
#include <chrono>
#include <numeric>
#include <vector>

using FunctorType = std::function<void(const itk::ImageRegion<2>&)>;
namespace
{
  volatile itk::ImageRegion<2> imageRegion;

  void CallStdFunction(FunctorType funcP, const itk::ImageRegion<2>& region)
  {
    funcP(region);
  }

  template <typename TFunction>
  void CallFunctionTemplate(TFunction funcP, const itk::ImageRegion<2>& region)
  {
    funcP(region);
  }


}
int main()
{
  constexpr int n{ 10'000'000 };

  volatile int result{};


  for (const bool bTemplate : {false, true})
  {
    using namespace std::chrono;
    const auto timePoint = high_resolution_clock::now();

    if (bTemplate)
    {
      for (int i{}; i < n; ++i)
      {
        CallFunctionTemplate([&result](const itk::ImageRegion<2>& region) {result += region.GetSize()[1]; }, itk::ImageRegion<2>{});
      }
    }
    else
    {
      for (int i{}; i < n; ++i)
      {
        CallStdFunction([&result](const itk::ImageRegion<2>& region) {result += region.GetSize()[1]; }, itk::ImageRegion<2>{});
      }
    }

    std::cout << " Duration: "
      << duration_cast<duration<double>>(high_resolution_clock::now() - timePoint).count() << " seconds" << std::endl;
  }

  return result;
}