Class App

example/polymorphism/concepts.cpp:23–30

requires Drawable

/*<<Static polymorphism - concepts>>*/
template <Drawable TDrawable = class Drawable>  // requires Drawable<TDrawable>
class App {
 public:
  explicit App(const TDrawable drawable) : drawable{drawable} {}
  void draw(std::ostream& out) const { drawable.draw(out); }

 private:
  const TDrawable drawable;
};

struct Square {
  void draw(std::ostream& out) const { out << "Square"; }