NetNews Usenet Archive 1992 #20/NN_1992_20.iso/spool/comp/lang/cplus/13639

Internet Message Format | 1992-09-14 | 2.8 KB

Path: sparky!uunet!sun-barr!olivea!spool.mu.edu!agate!agate!matt
From: [e-mail] (Matt Austern)
Newsgroups: comp.lang.c++
Subject: Re: Proposal: Subscripting with multiple arguments
Message-ID: <[e-mail]>
Date: 14 Sep 92 23:19:55 GMT
References: <[e-mail]>
Reply-To: [e-mail]
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
Lines: 40
NNTP-Posting-Host: physics.berkeley.edu
In-reply-to: [e-mail]'s message of 14 Sep 92 18:29:42 GMT

In article <[e-mail]> [e-mail] (Michael R Haggerty) writes:

> I have been using C++ for numerical work, and one of the changes which would
> be most useful would be to allow the subscription operator to take multiple
> parameters.  This would make it much simpler to define classes for multi-
> dimensional matrices without the nuisance of having to define a helper class.
> The concept should not be such a shock to anyone, as the subscript operator
> is already allowed to take non-integer arguments so is already significantly
> extended from the C subscript operator.

I've also occasionally wished that I could define, say,
    operator[](int,int,int),
and for the same reason: multi-dimensional arrays.  I haven't wished
for it very often, though, because that isn't really the syntax that I
want for a multi-dimensional array anyway; I would much rather access
an array element using the syntax A[i][j] than using the syntax
A[i,j].  After all, the A[i][j] syntax is what you would use if you
were using built-in data types instead of classes, and it's nice to
keep some things the same when defining a class.  (For that matter,
there isn't really anything wrong with the syntax A(i,j), either.)

Of course, if you want to use the A[i][j] syntax then you have to
define a helper class, but that's not too horrible a burden: you
really shouldn't be defining array classes very often anyway, but
should just do it once, and do it right.

What I find to be a bigger problem, actually, is designing an array
class that works for arrays with an arbitrary number of dimensions.
There's no problem with defining the classes Array1, Array2,
Array3,..., and that's exactly what I've done, but it's annoying and
inelegant.  Has anyone out there come up with a good definition for
arrays with an arbitrary number of dimensions? ("Good," in this
context, means specifically that array reference is sufficiently well
optimized that an intelligent programmer wouldn't mind using this
class in an inner loop.)
--
Matthew Austern                   Just keep yelling until you attract a
[phone]                    crowd, then a constituency, a movement, a
[e-mail]                faction, an army!  If you don't have any
[e-mail]         solutions, become a part of the problem!