"The last feature": overridable methods in interfaces

[retard]

Mon, 08 Feb 2010 12:59:33 -0500, Michel Fortin wrote:

> On 2010-02-08 11:58:53 -0500, retard <re at tard.com.invalid> said:
> 
>> Mon, 08 Feb 2010 07:03:43 -0600, Andrei Alexandrescu wrote:
>> 
>>> I think lack of state is indeed the only difference. The multiple
>>> inheritance bit makes all the difference, so I think abstract classes
>>> are not enough. A designer who wants to define some methods in an
>>> interface is forced at design time to choose an abstract class over an
>>> interface, thus severely limiting clients.
>> 
>> I really wonder why you're doing this. NIH. Ever heard or Scala and
>> traits? I'm sorry, but you didn't invent this feature - giving some
>> kind of attribution would be honest. I can imagine how this proposal
>> goes forward. Suddenly D 2 gets almost exactly the same feature (+
>> contracts) as Scala has had for a long time and somehow you get all the
>> credit in the practical (C++/D) PL community.
> 
> Hum, where did Andrei claimed he invented this?
> 
> To me who knows well Objective-C, this looks like an adaptation to D of
> the informal protocol concept, which was then superseded by optional
> methods in formal protocols in Objective-C 2.0. This pattern is used a
> lot in Objective-C, even though it's implemented differently and is more
> powerful due to categories.
> 
> Also, I don't know much about SmallTalk, but given SmallTalk was the
> inspiration for Objective-C I wouldn't be surprised to see this there
> too.
> 
> It's nice to give attribution, but where do we stop? Can you say you
> know for sure what was the real inspiration for this?

No, I don't know the original source. Multiple inheritance is an old and 
widely known problem. I just meant that instead of bikeshedding here and 
reinventing everything from scratch, everyone interested in the topic 
should take a look at Scala's traits since traits basically are 
interfaces extended with function bodies. Scala also has a solution to 
the conflicting multiply inherited methods. I just mentioned Scala 
because it's also a C inspired object oriented language and this feature 
proposal is more or less 90% the same concept as traits, both 
syntactically and semantically.