Should certain abstract classes be instantiable?

[Andrei Alexandrescu]

Jarrett Billingsley wrote:
> On Thu, Oct 1, 2009 at 4:30 PM, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> 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?
> 
> Uh... why?

Because I want to give a good argument one way or another in TDPL. FWIW, 
"I can't imagine why you'd ever..." or "Never needed that" are not 
strong enough arguments.

Andrei