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From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.lang.misc
Subject: Re: CHALLENGE: heterogeneous collections
Message-ID: <24673:Mar2802:15:1091@kramden.acf.nyu.edu>
Date: 28 Mar 91 02:15:10 GMT
References: <48805@nigel.ee.udel.edu> <7689:Mar2623:28:5091@kramden.acf.nyu.edu> <1991Mar27.164605.24547@visix.com>
Organization: IR
Lines: 22

In article <1991Mar27.164605.24547@visix.com> adam@visix.com writes:
> Let me get this straight.  To construct a heterogeneous list of M
> items each guaranteeing N operations, I need to waste space for M*N
> function pointers?

No, because you can just have a single ``class'' structure with the N
function pointers, and keep just one pointer per ``object.'' But this
extra layer is pointless for small problems, and I didn't bother putting
it in.

> And I need to write an explicit constructor for every kind of list?

That depends on what you mean by ``explicit.'' If you have several types
each supporting some sort of redraw operation, and you want to set up a
list of redrawable things, then you do have to say the correspondence
between ``redrawable'' and the redrawing for each type. Other posters
have mentioned how in object-oriented languages you can make the
redrawing class either a superclass or a subclass of all the classes in
question; either way provides the necessary correspondence, but I
wouldn't say it's explicit.

---Dan