Re: Derivable singleton implementation

"Igor Tandetnik" <>
Mon, 28 Dec 2009 10:23:52 -0500
Faisal wrote:

I have a generic Singleton class.
template <class TYPE>
class CSingleTon
virtual ~CSingleTon(){}
static TYPE* Instance()
if( NULL == m_pInstance )
m_pInstance = new TYPE();
return m_pInstance;
static void Destroy()
delete m_pInstance;
m_pInstance = NULL;
static TYPE* m_pInstance;
template <class TYPE>
TYPE* CSingleTon<TYPE>::m_pInstance = NULL;
#define SET_SINGLETON( classname ) friend class CSingleTon<classname>;
//end of file Singleton.h
And I uses this class to create singletone classes
class CGlobalDataStore : public CSingleTon<CGlobalDataStore>
This is working correctly.
Now I want to derive a class from CGlobalDataStore( which is also

Don't derive from CSingleTon in the first place. You can do something =
like this:

class CGlobalDataStore {
  static CGlobalDataStore* Instance() {
    return CSingleTon<CGlobalDataStore>::Instance();

class CAnotherStore: public CGlobalDataStore {
  static CAnotherStore* Instance() {
    return CSingleTon<CAnotherStore>::Instance();

I don't quite see how this design makes sense though. You now have two =
singletons - one CGlobalDataStore and one CAnotherStore - so there are =
two instances of CGlobalDataStore in the program (one on its own and one =
as a subobject of CAnotherStore), which kind of defeats the point of it =
being a singleton.
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not =
necessarily a good idea. It is hard to be sure where they are going to =
land, and it could be dangerous sitting under them as they fly overhead. =
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