cs nov 6

shape s cannot be declared as the contructor for shape is protected...
Triangle T ( inherited for shape) is ok  since derived classes can use protected member functions such as the constructor..



Triangle

     -add(POint);  vector<Point> points


Polygon also inherits everything from shape. it also has a vector of points and and has the add method for it.

struct Triangle : Shape
{
  Triangle(p1,p2, p3, c)
  :
  {
    p.add(point1);
  };
}

struct Polygon : Closed_polyline {
  {
      void add(Point p);  // add is different from shape so it is being overridden from Shape, there is an invariant no parallels and intersection..
    void draw_lines() const;
 };


open_polyline <- Closed_polyline<- Polygon

Polygon <- Triangle  (so not needing a separate storage for points.

public :

Point point(int i) const {returns points[i]; }  // read only access to points vector in the shape class.


Triangle - > Point (Association relationship, Point does not know about Triangle but Triangle can see point)

violet -- metauml diagram

Inheritance is a relationship between classes.

Association/Aggregation/Composition -- relationship between class and the objects in it or between objects. specific/concrete.

3 Relationships
is-a
has-a
uses

After refactoring ::

class Triangle : Polygon
{
    Triangle ( )
  {
       this.add();
   // the number of points cannot be more than 3;
}