Question

Aside from having a pure virtual function, is there a way to prevent an instantiation of an abstract base class?

I can do this:

class BaseFoo
{
    virtual void blah() = 0;
};

class Foo : public BaseFoo
{
    virtual void blah() {}
};

but I’d like to avoid a vtable. (as per my other question about virtual destructors)

Microsoft ATL has ATL_NO_VTABLE to accomplish this (or at least I think that’s what it does…)

Answer 1

A really obvious way is to declare a protected constructor, and to declare public constructors in the non-abstract derived classes.

This of course shifts the burden of corectness to the derived classes, but at least the base class is protected.