A simple example on C++ functor

functor_example.cc

#include <iostream>

class Image {
};
  
class blur {
 public:
  blur(double factor) : factor_(factor) {}
  
  void operator()(Image & img) const   {
    std::cout << "Bluring image using factor=" << factor_ << "\n";
  }

 private:
  double factor_;
};

class compress {
 public:
  compress(int width, int height) : width_(width), height_(height) {}
  
  void operator()(Image & img) const   {
    std::cout << "Compressing image to new size (" << width_ << ", " << height_ << "\n";
  }

 private:
  int width_, height_;
};

int main() {
  Image img;
  blur(1.0)(img);
  compress(100, 200)(img);
}

Build and run on my Mac

$ clang++ functor_example.cc -o functor_example  && ./functor_example
Bluring image using factor=1
Compressing image to new size (100, 200