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From: thant@horus.sgi.com (Thant Tessman)
Newsgroups: comp.object,comp.lang.c++
Subject: Re: Understanding the Object-Oriented Life-Cycle
Message-ID: <1403@odin.SGI.COM>
Date: 13 Nov 89 17:03:19 GMT
References: <20481@brunix.UUCP> <5026@internal.Apple.COM> <315@shrike.AUSTIN.LOCKHEED.COM> <654@nastar.UUCP> <44454@sgi.sgi.com>
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Reply-To: thant@horus.sgi.com (Thant Tessman)
Organization: Silicon Graphics, Inc.
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In article <20481@brunix.UUCP>, sdm@brunix (Scott Meyers) writes:
> Hmmm, what about using MI so that anything that will ever go on a list
> inherits from a class "Listable" that defines the appropriate virtual
> comparison operators?  Then your lists would consist of pointers to objects
> of type Listable.  It should be type-safe because only Listable objects can
> end up on lists, and all Listable objects have the necessary comparison
> operators appropriately defined.  No macros needed, and having a single
> object on multiple lists is no problem.  Am I overlooking something?
> 
> Scott
> sdm@cs.brown.edu

I don't know.  I think what you describe is fine for doing 'listy' type things
on lists.  But, in my case, what I really wanted was a list of Goobers that 
I could do 'goobery' things with as well as 'listy' things.  In that case, I
needed to overload my iterator to return the correct type.  This guarantees
that I can't to 'goobery' things to any old list, just to lists of
Goobers.  Since 
List was a base class of Goober (I didn't really call it Goober) all the
list stuff
automatically worked and was type safe.

And even this won't solve the problem of allowing a list where each element 
can be anything.  (I don't even think dynamic typing is a solution.  What 
does the program written in a dynamic typing language do when the type 
is wrong that you couldn't get a c++ program to do just as easily?)

thant

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There are 336 dimples on the standard golf ball.