factory method in C++

```
#include <iostream>
#include <string>

using namespace std;

class Shape {
public:
   virtual void Draw() = 0;
   static Shape* ShapeFactory(string type);
};

class Circle : public Shape {
public:
   void Draw() { cout << "I am circle" << endl; }
   friend class Shape;
};

class Square : public Shape {
public:
   void Draw() { cout << "I am square" << endl; }
   friend class Shape;
};

Shape* Shape::ShapeFactory(string type) {
    if ( type == "circle" ) return new Circle();
    if ( type == "square" ) return new Square();
    return NULL;
}

int main(){
   Shape* obj1 = Shape::ShapeFactory("circle");
   Shape* obj2 = Shape::ShapeFactory("square");
   obj1->Draw();
   obj2->Draw();
}

/*
I am circle
I am square
*/
```
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