Protoype Design Pattern Link Issue

Hi All,

I am using the prototype design pattern to design a static library in linux.

the class architecture looks like below:

Code:

---

//Product.h
class Product
{
public:
  virtual ~Product() {}
  virtual Product* clone() const = 0;
  static Product* makeProduct(string type);
  static Product* addPrototype(string type, Product* p);
  static map<string, Product*>& getMap()
  {
        static map<string, Product*> protoTable;
        return protoTable;
  }
};

#define IMPLEMENT_CLONE(TYPE) \
  Product* clone() const { return new TYPE(*this); }

#define MAKE_PROTOTYPE(TYPE) \
  Product* TYPE ## _myProtoype = \
      Product::addPrototype(#TYPE, new TYPE());

---

Code:

---

// product1.h
#include "product.h"

class Product1: public Product
{
public:
  IMPLEMENT_CLONE(Product1)
  // etc.
};

---

Code:

---

// product1.cpp
#include "product1.h"
MAKE_PROTOTYPE(Product1)
// etc.

---

Code:

---

//in test.cpp
int main()
{
    Product* pObj = Product::makeProduct("Product1");
  // etc.
}

---

all subclass of Product will exist in their own .o file, like Product1.o, Product2.o ......
and they will be grouped into a libProduct.a static lib.

Code:

---

gcc test.o libProduct.a

---

problem is that my test main program it does not know the existence of Product1 and Product2 for example, then Product1.o and Product2.o will not be linked. And when I was trying to create the Prodcut1 object as in the test main function, it will return NULL pointer.

Your ideas and expertise advice is very appreciated.

Thanks a lot in advance!
sandodo

you havent added it (the product) to the protoTable before you try and make it.

you can do it like this:

Code:

---

Product::getMap()["Product1"] = new Product1;

---

the getMap code and the table should really be moved to a factory class though - it's not strictly part of the product.