Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!think.com!mintaka!ogicse!unmvax!bbx!tantalum!tom
From: tom@eds.com (Tom H. Meyer)
Newsgroups: comp.lang.eiffel
Subject: Re: Suggestion for use of Void
Summary: Void comments and a new question
Message-ID: <4106@tantalum.UUCP>
Date: 3 Dec 90 22:19:21 GMT
References: <1037@tetrauk.UUCP>
Sender: usenet@tantalum.UUCP
Reply-To: tom@ozmium.UUCP (Tom H. Meyer)
Organization: EDS Research
Lines: 46

In article <1037@tetrauk.UUCP> rick@tetrauk.UUCP (Rick Jones) writes:

>It would be far cleaner to be able to write:
>
>			excep.Create (code, Void) ;
>
>A Void of course conforms to any class type, so it is syntactically valid
>anywhere an object reference is required.
>
>This raises the interesting issue of forms such as:
>
>	obj_ref := Void			equivalent to	obj_ref.Forget
>
>	if obj_ref = Void then		equivalent to	if obj_ref.Void then

I have often run into this problem and wished for exactly this solution. Oh,
well. So much for sparking a controversy :-)

>...  Given the opportunity, I would in fact replace the following
>as well:
>
>	a.Create (params)		a := Create A_CLASS (params)

I dislike this on the grounds that it would *require* that 'Create' be a
keyword. I hope to see the day when classes can have more than one
creation routine and this seems to disallow it.

Since you asked for some net traffic and we're talking about programming,
I would like feed back on how some others out there would do the following:

Suppose I have some class which which has a list of generic objects and
my application needs to examine every item on the list and perform 
different actions based on the actual type of the items on the list.

My solution is a sequence of reverse assignment attempts to,
first, determine the actual type of the object, and, second, have a
local object of the correct type to access the specific object's features.

I've heard that this is poor style but I've never been able to see a
better way to do it. Supposedly, there is some way of designing the classes
so that this isn't necessary. Can anyone give me an example?


tom meyer, EDS Research               | If I don't see you in the future
...uunet!tantalum!tom                 | I'll see you in the pasture
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