派生类中的反射工厂C++无法访问受保护的方法

受到回答Johannes Schaub的回答的启发，我试图实现一个反射工厂。这个想法是，您可以通过将类的名称传递给一个方法来创建对象，该方法在堆上创建相关对象并返回指向公共基类的指针。如有必要，使用 dynamic_cast 和 RTTI，可以将对象转换回其原始类型。应该能够使用反射工厂，如下所示：

// Base is the base class of all objects to create.
class Factory: public AbstractFactory<Base>
{
public:
    Factory()
    {
        m_map["DerivedA"] = &AbstractFactory::createInstance<DerivedA>;
        m_map["DerivedB"] = &AbstractFactory::createInstance<DerivedB>; 
    }
};
int main()
{
    Factory factory;
Base *a = factory.Create("DerivedA");
DerivedA *aa = dynamic_cast<DerivedA*>(a);
    // etc..
}

到目前为止，我得到了这个工作。但是，下面的代码有两个主要问题。它很丑陋，如果我使抽象工厂的方法受到保护，它会抱怨它无法访问createInstance()方法。这是我不明白的。根据定义，派生类应该能够访问基类的受保护方法。我在VS 2008中测试了代码。进一步说明：我知道基类并不是真正抽象的，因为它不包含纯虚函数。我知道std：：function，但到目前为止我还没有使用它。也许我将来会这样做。

#include <iostream>
#include <map>
#include <typeinfo>
#include <string>
struct Base
{
    virtual std::string SayHello() = 0;
};
struct DerivedA: public Base
{
    virtual std::string SayHello() 
    {
        return "Hello from DerivedA";
    }
};
struct DerivedB: public Base
{
    virtual std::string SayHello() 
    {
        return "Hello form DerivedB";
    }
};
/**
 * @brief Reflective Factory class. Creates objects of classes which derive from
 *        a common base class.
 *
 */
template<class BASE_T>
struct AbstractFactory
{
// Macro to call ptrs to member functions as recommended in the C++ FAQ lite.
// http://www.parashift.com/c++-faq-lite/pointers-to-members.html
#define CALL_MEMBER_FN(object, ptrToMember) ((object).*(ptrToMember))
    // Recall funcion ptr syntax for members: ReturnType (class::*) (Arguments)
    // using a typedef makes it easier..
    typedef BASE_T*  (AbstractFactory::*func_ptr_type) ();
    // retType^ ClassName^ AliasName^  Arguments^
    typedef std::map<std::string, func_ptr_type> map_type;
    template<typename DERIVED_T> 
    BASE_T * createInstance() 
    { return new DERIVED_T; }
    map_type m_map;
    /**
     * @brief Creates an object from a class with the name given as string.             
     */
    BASE_T * Create(std::string className)
    {
        // Note the last () at the end.
        return CALL_MEMBER_FN(*this, m_map[className])();
    }
#undef CALL_MEMBER_FN
};
class Factory: public AbstractFactory<Base>
{
public:
    Factory()
    {
        m_map["DerivedA"] = &AbstractFactory::createInstance<DerivedA>;
        m_map["DerivedB"] = &AbstractFactory::createInstance<DerivedB>; 
    }
};
int main()
{
    Factory factory;
    Base *a = factory.Create("DerivedA");
    DerivedA *aa = dynamic_cast<DerivedA*>(a);
    std::cout << typeid(a).name()  << std::endl;
    std::cout << typeid(*a).name()  << std::endl;
    std::cout << typeid(aa).name() << std::endl;
    std::cout << aa->SayHello() << std::endl;
    std::cin.get();
    return 0;
}

更新

我使用 VS 2008 得到的确切错误是（在德语中，对不起不是我的选择......

1>------ Erstellen gestartet: Projekt: ReflectiveFactory, Konfiguration: Debug Win32 ------
1>Kompilieren...
1>main.cpp
1>.main.cpp(82) : error C2248: "AbstractFactory<BASE_T>::createInstance": Kein Zugriff auf protected Member, dessen Deklaration in der AbstractFactory<BASE_T>-Klasse erfolgte.
1>        with
1>        [
1>            BASE_T=Base
1>        ]
1>        .main.cpp(55): Siehe Deklaration von 'AbstractFactory<BASE_T>::createInstance'
1>        with
1>        [
1>            BASE_T=Base
1>        ]
1>.main.cpp(83) : error C2248: "AbstractFactory<BASE_T>::createInstance": Kein Zugriff auf protected Member, dessen Deklaration in der AbstractFactory<BASE_T>-Klasse erfolgte.
1>        with
1>        [
1>            BASE_T=Base
1>        ]
1>        .main.cpp(55): Siehe Deklaration von 'AbstractFactory<BASE_T>::createInstance'
1>        with
1>        [
1>            BASE_T=Base
1>        ]