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From: brnstnd@stealth.acf.nyu.edu
Newsgroups: comp.lang.misc
Subject: Re: Pointers as 3-tuples
Message-ID: <296:Apr1105:06:4490@stealth.acf.nyu.edu>
Date: 11 Apr 90 05:06:44 GMT
References: <S4U2APBggpc2@ficc.uu.net> <14327@lambda.UUCP>
Reply-To: brnstnd@stealth.acf.nyu.edu (Dan Bernstein)
Distribution: usa
Organization: IR
Lines: 33
X-Original-Subject: Re: JLG's flogging of horses

In article <14327@lambda.UUCP> jlg@lambda.UUCP (Jim Giles) writes:
> From article <S4U2APBggpc2@ficc.uu.net>, by peter@ficc.uu.net (Peter da Silva):
  [ Peter once again reminds Jim that pointers can be implemented to ]
  [ reliably detect what ANSI C calls illegal pointer operations ]
> In fact, what you are recommending is a constraint on pointers which
> removes one of the _only_ features that I thought pointers were useful
> for.

Say what? Jim, are you saying that you thought pointers were only useful
for operations that ANSI C calls illegal? Once again, the ``constraint''
embodied by, say, pointer 3-tuples changes absolutely none of the ANSI C
pointer semantics---because that constraint *is* the semantics. I must
admit I've never found any use for going outside those semantics, except
in device drivers.

> Multidimensional arrays
> are NOT arrays-of-arrays.  The subscripts of a multidimensional
> array are independent and carry _equal_ weight.

Both assembly code and mathematics say otherwise: at some level of
specification (the opposite of abstraction), a multidimensional array
really is an array of arrays. I agree, the user often doesn't think of
it that way; but it's still the truth.

> > 	INTEGER A(10)
> > 	CALL PROC(A,A)
> Not necessarily broken.  Only if PROC modifies one or more of its
> arguments.

Note that Fortran has no way to express that concept explicitly, while C
can declare const int *A. Hmmm, shall we start flogging this horse too?

---Dan