Xref: utzoo comp.lang.misc:7270 comp.object:3028
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From: richieb@bony1.bony.com (Richard Bielak)
Newsgroups: comp.lang.misc,comp.object
Subject: Re: CHALLENGE: heterogeneous collections
Message-ID: <1991Apr3.211414.25628@bony1.bony.com>
Date: 3 Apr 91 21:14:14 GMT
References: <1991Mar25.220525.11087@leland.Stanford.EDU> <CIMSHOP!DAVIDM.91Mar28192651@uunet.UU.NET> <521@eiffel.UUCP> <CIMSHOP!DAVIDM.91Apr1224716@uunet.UU.NET>
Reply-To: richieb@bony1.UUCP (Richard Bielak)
Distribution: comp
Organization: Bank of New York
Lines: 54

In article <CIMSHOP!DAVIDM.91Apr1224716@uunet.UU.NET> cimshop!davidm@uunet.UU.NET (David S. Masterson) writes:
[...]
>
>I really hate the idea of contradicting Bertrand Meyer as I'm probably getting
>in over my head. 

Don't blame you! :-)
[...]

>On the other hand:
>
>	h_collection: COLLECTION [void]		/* or is it 'void*'? */
>
>might be a *truly* heterogeneous collection (assuming objects entered into the
>collection can be implicitly cast to VOID), but (going back to the original
>question) how useful would it be since all clues as to type and protocol of
>objects in the collection are removed?

The generic collection should really be declared as:

        h_collection: COLLECTION [ANY];

as any class in Eiffel is an heir of ANY.

The following trick can be used to do things with objects in such
a collection.

        my_weird_object : MY_WEIRD_CLASS;

        ....

        my_weird_object ?= h_collection.next_item;

        -- above line gets the next item from the collection
        -- and does a "reverse" assigment to my variable.
        -- this assigment will only work, if the type on
        -- the right is of type MY_WEIRD_CLASS (or a descendant)
        -- otherwise, Void is returned. 
        -- so,

        if not my_weird_object.Void then
                -- got a weird_object_here, do what you need to
                ....
        end;



...richie "What does a virtual void look like?"

-- 
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