Marcus, Rats :) You've stolen my thunder. Actually, I won't go as far as to say "never," but I agree. There are places in Squeak that inherit from collections or put methods in Object, and it sure looks as though the programmer didn't know any better. In fairness, it might have been intended to minimize the chance of runtime errors. Think about it: by wrongly inheriting from OrderedCollection, one is freed from having to delegate its methods (it's not correct, but can seem wise to a beginner or expedient an experienced programmer with poor tools). Mess around with the internals of the user interface, and sliding a method up the hierarchy can avoid a meltdown. These things were all the more true before the days of exception handling. By all means, we should fix these things as we find them. Bill -----Original Message----- From: pharo-project-bounces@lists.gforge.inria.fr [mailto:pharo-project-bounces@lists.gforge.inria.fr] On Behalf Of Marcus Denker Sent: Wednesday, February 03, 2010 10:53 AM To: Pharo-project@lists.gforge.inria.fr Cc: Laval Jannik Subject: Re: [Pharo-project] DirectoryEntry does not inherit from ArrayedCollection [WAS] Re: [squeak-dev] 3.11 questions On Feb 3, 2010, at 4:43 PM, Mariano Martinez Peck wrote:

On Wed, Feb 3, 2010 at 4:34 PM, Chris Muller <asqueaker@gmail.com> wrote:

4) I have refactored DirectoryEntry to no longer inherit from ArrayedCollection. Is this an improvement with any community interest?

Do you think this is interesting ? What are the benefits of such change ?

Jannik: do we kill a cycle dependency or something with this change ?

You should never inherit from collections. The problem is that with this, you are depending on the internal working of the collection. Especially objects that model a domain object (like a Directory related thing) should *never* inherit from a collection. Only if you need a special *kind* of collection (technically), it might be interesting to do a subclass of a collection (see MethodDictionary). If you need a collection, you *use* a collection. (you put a standard collection as an instance var). It's very tempting to use inheritance to aquire behavior. But in most cases, it is wrong to use it. You can see this abuse of inheritance very often in Squeak... e.g. Scanner is the superclass of Parser, there are subclasses of SystemWindow (!!), things like that. Bad. Marcus -- Marcus Denker -- http://www.marcusdenker.de INRIA Lille -- Nord Europe. Team RMoD. _______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project

On 3 February 2010 18:12, Marcus Denker <marcus.denker@inria.fr> wrote:

On Feb 3, 2010, at 5:03 PM, Schwab,Wilhelm K wrote:

...

Marcus,

Rats :)  You've stolen my thunder.  Actually, I won't go as far as to say "never," but I agree.  There are places in Squeak that inherit from collections or put methods in Object, and it sure looks as though the programmer didn't know any better.

And partly, this was because it was done a very long time ago... back than, it was not known how to program with this newly invented object things. Even by the people who invented it! It's often that others, who than use it, learn how to use it better than the creators.

The same will happen with everything we will invent (if we invent anything, that is :-) ).

+100 the good thing is, that we're free to change this. While java people got stuck with sealed stuff forever :)

       Marcus

-- Marcus Denker  -- http://www.marcusdenker.de INRIA Lille -- Nord Europe. Team RMoD.

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