C++ static virtual members?

cvb picture cvb · Nov 30, 2009 · Viewed 107.7k times · Source

Is it possible in C++ to have a member function that is both static and virtual? Apparently, there isn't a straightforward way to do it (static virtual member(); is a compile error), but is there at least a way to achieve the same effect?

I.E:

struct Object
{
     struct TypeInformation;

     static virtual const TypeInformation &GetTypeInformation() const;
};

struct SomeObject : public Object
{
     static virtual const TypeInformation &GetTypeInformation() const;
};

It makes sense to use GetTypeInformation() both on an instance (object->GetTypeInformation()) and on a class (SomeObject::GetTypeInformation()), which can be useful for comparisons and vital for templates.

The only ways I can think of involves writing two functions / a function and a constant, per class, or use macros.

Any other solutions?

Answer

Adam Rosenfield picture Adam Rosenfield · Nov 30, 2009

No, there's no way to do it, since what would happen when you called Object::GetTypeInformation()? It can't know which derived class version to call since there's no object associated with it.

You'll have to make it a non-static virtual function to work properly; if you also want to be able to call a specific derived class's version non-virtually without an object instance, you'll have to provide a second redunduant static non-virtual version as well.