Simple builder example in CXX

shape_example.cxx

/* Simon psyomn Symeonidis 2015
 * g++ -std=c++11 example.cpp
 */
#include <iostream>
#include <string>
#include <cstddef>

using std::string;
using std::cout;
using std::endl;

class Shape {
  public:
    virtual int area() = 0;
    virtual ~Shape() {};
    string label() { return _label; }
  protected:
    string _label;

  friend class ShapeBuilder;
};

class Rectangle : public Shape {
  public:
    virtual int area() {
      return _x * _y;
    }
  private:
    int _x;
    int _y;

  friend class ShapeBuilder;
};

class Square : public Shape {
  public:
    virtual int area() {
      return _side * _side;
    }
  private:
    int _side;

   friend class ShapeBuilder;
};

class Circle : public Shape {
  public:
    virtual int area() {
      return int(3.142 * (_radius * _radius));
    }
  private:
    int _radius;

  friend class ShapeBuilder;
};

class ShapeBuilder {
  public:
    ShapeBuilder() : _x(0), _y(0), _side(0), _radius(0) {}

    ShapeBuilder* x(int __x) {
      _x = __x;
      return this;
    }

    ShapeBuilder* y(int __y) {
      _y = __y;
      return this;
    }

    ShapeBuilder* radius(int __r) {
      _radius = __r;
      return this;
    }

    ShapeBuilder* side(int __s) {
      _side = __s;
      return this;
    }

    Shape* finalize() {
      if (_x != 0 && _y != 0) {
        auto rect = new Rectangle();
        rect->_x = _x;
        rect->_y = _y;
        rect->_label = "rectangle";
        return rect;
      }
      else if (_side != 0) {
        auto sqr = new Square();
        sqr->_side = _side;
        sqr->_label = "square";
        return sqr;
      }
      else if (_radius != 0) {
        auto circ = new Circle();
        circ->_radius = _radius;
        circ->_label = "circle";
        return circ;
      }
      return nullptr;
    }

  private:
    int _x;
    int _y;
    int _side;
    int _radius;
};

int main(void) {
  Shape
    *rec = ShapeBuilder().x(10)->y(20)->finalize(),
    *cir = ShapeBuilder().radius(10)->finalize(),
    *sqr = ShapeBuilder().side(4)->finalize();

  cout << rec->label() << " area: " << rec->area() << endl;
  cout << cir->label() << " area: " << cir->area() << endl;
  cout << sqr->label() << " area: " << sqr->area() << endl;

  delete rec;
  delete cir;
  delete sqr;

  return EXIT_SUCCESS;
}
/** output:
 * rectangle area: 200
 * circle area: 314
 * square area: 16
 */