Re: Pure virtual, forced implementation, and base class methods

.. So what we want to do is expose a class that's got some methods in
that are pure virtual, so you have to override them - but they're
incompletely implemented in the base class. There's some useful stuff in
the base class implementation, just not enough. A diagnostic dump
function is an example.

The exposed class is the tip of a hierarchy. It is _not_ the one with
the implementation. This minimal example shows roughly what we have. C
is the exposed class; D is locally derived from it. In D we want to call
into a base class method; B forces us to implement that method. It looks
as though in the most derived method we have to know which of the
classes in the hierarchy has an implementation in order to call it. Yet
if we leave out the declaration that forces us to implement a derived
method we can call through _without_ knowing which of the classes
implements it.

Is this just the way it is, an MS bug, or is there a better way?

Andy

struct A
{
virtual void m()
{
};
};

struct B: public A
{
// Uncomment this to get link failures
// virtual void m() = 0;
};

struct C: public B
{
};

struct D: public C
{
virtual void m()
{
C::m();
// without the pure virtual declaration this calls A::m
// with the declaration it tries to call B::m
};
};

void main()
{
D().m();
}