Decorator.cpp

#include <string>
#include <sstream>
#include <iostream>

struct Shape {
  virtual std::string str() const = 0;
};

struct Circle : Shape {
  float radius;

  Circle(const float radius) : radius{radius} {}
  Circle() : radius{0} {}

  void resize(float factor) { radius *= factor; }

  std::string str() const override {
    std::ostringstream oss;
    oss << "A circle of radius " << radius;
    return oss.str();
  }
};

template<typename T>
struct ColoredShape : T {
  std::string color;

  template<typename...Args>
  ColoredShape(std::string color, Args ...args)
      : T(std::forward<Args>(args)...), color{color} {}

  std::string str() const override {
    std::ostringstream oss;
    oss << T::str() << " has the color " << color;
    return oss.str();
  }
};

int main() {
  Circle C{0.5};
  ColoredShape<Circle> circle{"red" , 10};
  // circle.radius = 0.5;
  std::cout << "r= " << circle.str() << std::endl;

  return 0;
}