问为什么一个可序列化的类必须有从类名中获取实例的函数？

EN

protected: 
    static CRuntimeClass* __stdcall _GetBaseClass(); 
public: 
    static CRuntimeClass classCMyClass; 
    static CRuntimeClass* __stdcall GetThisClass(); 
    virtual CRuntimeClass* GetRuntimeClass() const; 
    static CObject* __stdcall CreateObject();  
    friend CArchive& __stdcall operator>>(CArchive& ar, CMyClass* &pOb);

CObject* __stdcall CMyClass::CreateObject() 
{ 
    return new CMyClass; 
} 

extern AFX_CLASSINIT _init_CMyClass; 

CRuntimeClass* __stdcall CMyClass::_GetBaseClass() 
{ 
    return (CObject::GetThisClass()); 
}

__declspec(selectany) CRuntimeClass CMyClass::classCMyClass = 
{ 
    "CMyClass", sizeof(class CMyClass), (0x80000000) | 1, 
    CMyClass::CreateObject, &CMyClass::_GetBaseClass, 0, &_init_CMyClass 
}; 

CRuntimeClass* __stdcall CMyClass::GetThisClass() 
{ 
    return ((CRuntimeClass*)(&CMyClass::classCMyClass)); 
} 

CRuntimeClass* CMyClass::GetRuntimeClass() const 
{ 
    return ((CRuntimeClass*)(&CMyClass::classCMyClass)); 
} 

AFX_CLASSINIT _init_CMyClass((CMyClass::GetThisClass())); 

CArchive& __stdcall operator>>(CArchive& ar, CMyClass* &pOb) 
{ 
    pOb = (CMyClass*) ar.ReadObject((CMyClass::GetThisClass())); 
    return ar;
}