Should certain abstract classes be instantiable?

[Lionello Lunesu]

On 2-10-2009 4:30, Andrei Alexandrescu wrote:
> Consider:
>
> class A {
> abstract void fun() {}
> }
>
> The class defines a function that is at the same time abstract (so it
> requires overriding in derivees) and has implementation.
>
> Currently the compiler disallows creation of objects of type A, although
> technically that is feasible given that A defines the abstract method.
>
> Should A be instantiable? What designs would that help or hinder?
>
>
> Andrei

If it were instantiable, what would be the difference between "abstract" 
and "virtual"?

L.