Should certain abstract classes be instantiable?

[Jeremie Pelletier]

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

What's the point of marking fun() abstract if it has an implementation, 
I thought the compiler disallowed that.