工厂设计模式问题

Question

Suppose there is a factory as below. I would like to know if it is possible not to include ObjectA.h and ObjectB.h.

directory structure
factory

|-----ObjectA

|-----ObjectB

Since I don't want to include the header file in the sub-directory, is there any way to do so? And if there is a new objectC, it does not need to modify the factory class. it will automatically create ObjectC if the type is "TypeC".

#include "ObjectA.h"
#include "ObjectB.h"

object* create(const string& type)
{
    if (type == "typeA")
    {
       return new ObjectA();
    }
    else
    {
       return new ObjectB();
    }
};

Answer 1

Yes, separate the implementation to an implementation file and only include the files there, providing solely the function prototype in the header.

To actually call new ObjectA(); and new ObjectB(); you have to include the definitions in the calling site.

//factory.h
object* create(const string& type);

//factory.cpp
#include "factory.h"
#include "ObjectA.h"
#include "ObjectB.h"

object* create(const string& type)
{
    if (type == "typeA")
    {
       return new ObjectA();
    }
    else
    {
       return new ObjectB();
    }
};