NetNews Usenet Archive 1992 #26/NN_1992_26.iso/spool/comp/lang/misc/3499

Internet Message Format | 1992-11-05 | 2.4 KB

Path: sparky!uunet!gumby!yale!yale.edu!think.com!barmar
From: [e-mail] (Barry Margolin)
Newsgroups: comp.lang.misc
Subject: Re: Pointers
Date: 5 Nov 1992 18:58:16 GMT
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 35
Message-ID: <[e-mail]>
References: <[e-mail]> <[e-mail]> <[e-mail]>
NNTP-Posting-Host: telecaster.think.com

In article <[e-mail]> [e-mail] (J. Giles) writes:
>   Second: in both, you should avoid aliasing.  In the case of GO TO,
>   you should avoid branching to the same label for many disparate
>   reasons.  In the case of pointers, you should try to avoid have
>   two pointers to the same thing *at all*.

That's a silly guideline.  The most common reason to use pointers is
precisely *because* you need multiple references to the same data.  In
object-based programming, an object may be in different relationships with
other objects, and relationships are usually implemented as pointers
between objects.  For instance, in a family tree model, a person might have
pointers to its parents, children, and siblings; any particular person is
likely to be referenced by the children array of two parents and a parent
pointer of some children.

Your guideline suggests that the main reason for using pointers is to avoid
copying data (e.g. passing arguments by reference by passing a pointer).
While pointers are certainly useful for this (in languages that don't
provide better mechanisms, such as C++'s references), I hardly consider it
the raison d'etre of pointers.

In another article, someone pointed out that the most spaghetti structured
code tends to be Lisp, which doesn't have pointers.  While it's true that
Lisp doesn't have distinct pointer values, in some sense every value is
conceptually a pointer value, because of Lisp's object-based nature (most
Lisp dialects allow optimizations for numeric values that that allow them
to be treated as non-objects, though).  The only difference between Lisp
and other languages in this regard is that Lisp doesn't have an explicit
dereference operator, as dereferencing happens automatically.  The Lisp
expression (car a) is analogous to the C expression (cons *)a->car.
--
Barry Margolin
System Manager, Thinking Machines Corp.

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