You haven't demonstrated the capability of Generics though (which C doesn't really have, only a minimal version). For this particular example, C++ does function overloading on parameters which C cannot hence you need this silly Generic macro hack, it is not clear how much of a win it is. Reminds of the saying that C is the most dynamic programming language since it has void*

It is much cleaner in C++ where you don't need to declare two separate functions names like you did.

  #include <iostream>
  #include <cmath>

  struct Rectangle {
      double width;
      double height;
  };

  struct Circle {
      double radius;
  };

  double area(const Rectangle& rect) {
      return rect.width * rect.height;
  }

  double area(const Circle& circle) {
      return M_PI * circle.radius * circle.radius;
  }

  int main() {
      Rectangle rect{5.0, 3.0};
      Circle circle{2.5};

      std::cout << "Rectangle area: " << area(rect) << std::endl;
      std::cout << "Circle area: " << area(circle) << std::endl;
      return 0;
  }

Though, bear in mind that _Generic is not generic templating. Highly useful, but it's more of a macro.

You can run into issues with aliased types, or where types of the same size accidentally fall through into the wrong parts of the _Generic selector.