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Re: majority voting [message #65139 is a reply to message #65079]

Fri, 13 February 2009 01:31

Allan Whiteford
Messages: 117
Registered: June 2006

Senior Member

Fï¿½LDY Lajos wrote:
>
> On Thu, 12 Feb 2009, JD Smith wrote:
>
>> I'm not sure if this is intentionally or accidentally inconsistent,
>> but it is indeed very useful.
>
>
> It may be useful, but I think X=X+1, X+=1 and X++ should give the same
> result for any X. Most programmers use these interchangeably.
>

Lajos, JD,

I think X+=1 should give the same as X++ (which they don't). In a
vectorised form of ++ (which most languages don't have) you're saying:
"here's a list of things, increment them all by one", it's reasonable to
assume that if the same thing is repeated then it will be acted on twice.

X=X+1 more means, in my mind, "evaluate X+1 and set X to the result of
that evaluation" - it's clearer in my mind that everything on the right
of the = will happen before the set operation is performed.

I do agree, of course, that this difference could lead to confusion.

The issue is that many languages like C explicitly don't allow you to
change the same variable twice on one operation. Languages like Perl
positively encourage it. I've never seen a general statement about what
IDL can and can't do in this regard. I could argue that "++x[[0,0,1]]"
doesn't really fall into this category since we're only using one operator.

IDL doesn't have a formal specification like C (the manual doesn't
count) nor has anyone ever said (at least that I've heard) that the
implementation is the specification (like, say, Perl 5).

I remember the awful day when the result of "help,({a:[1]}).a" changed
and all my widget based code collapsed in a heap - I live in fear of
that day coming again so share your worries. It's possible that someone
will look at ++ and think they can split it across multiple cores - that
will be a bad day.

Maybe someone should write to ITTVIS and ask if they intended this as a
feature and if they can guarantee that it will remain. I'll do this and
report back.

Thanks,

Allan

> regards,
> lajos
>

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[Message index]

		majority voting By: Mort Canty on Wed, 11 February 2009 08:14
		Re: majority voting By: Allan Whiteford on Fri, 13 February 2009 01:31
		Re: majority voting By: David Fanning on Sat, 14 February 2009 08:44
		Re: majority voting By: JD Smith on Thu, 12 February 2009 14:45
		Re: majority voting By: Foldy Lajos on Thu, 12 February 2009 12:47
		Re: majority voting By: David Fanning on Thu, 12 February 2009 12:11
		Re: majority voting By: pgrigis on Thu, 12 February 2009 11:58
		Re: majority voting By: JD Smith on Thu, 12 February 2009 10:49
		Re: majority voting By: Mort Canty on Thu, 12 February 2009 07:45
		Re: majority voting By: JD Smith on Thu, 12 February 2009 07:08
		Re: majority voting By: David Fanning on Thu, 12 February 2009 05:43
		Re: majority voting By: Allan Whiteford on Thu, 12 February 2009 04:17
		Re: majority voting By: Mort Canty on Thu, 12 February 2009 01:15
		Re: majority voting By: JD Smith on Wed, 11 February 2009 15:20
		Re: majority voting By: ben.bighair on Wed, 11 February 2009 14:03
		Re: majority voting By: Allan Whiteford on Mon, 16 February 2009 04:11

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