Inheriting from Template Class

[g0dwyn]

Hey everyone,

While designing a Singleton class for an app I'm creating, I looked at the Ogre implementation of a Singleton (motivation and usage details here:http://www.ogre3d.org/wiki/index.php/Singleton) and created a template-based system. In order to make a class a Singleton, you simply inherit the Singleton class, like so:

class OnlyOne : public Singleton<OnlyOne>
{
...
}

The problem is that my compiler won't allow this sort of (semi) self-referential template nonsense, seeing as the OnlyOne class hasn't been properly declared. I tried forward declaration, but that didn't work either. Any other suggestions? Using MinGW 3.4.5

EDIT: topic name edited to better reflect the problem

[Disch]

That should work just fine. You just can't use an object of the derived type in the template. You have to use a pointer or a reference. I didn't even need to forward declare it:

template <typename T>
class Singleton
{
public:
  static T& Instance();  // note: reference
};

//----------------------

class OnlyOne : public Singleton<OnlyOne>  // works just fine
{
};

[g0dwyn]

Strange...I'm still getting problems with it, despite the use of a reference. Which compiler are you using?

[g0dwyn]

Ah, wait, I think I got it. Thanks for your help Disch.

[g0dwyn]

Turns out it was all due to unrelated namespace errors. Thanks for your time!