Should certain abstract classes be instantiable?

[Andrei Alexandrescu]

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