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Re: Commons, Was: can i place a job advert [message #28217 is a reply to message #28126]

Mon, 26 November 2001 11:21

Richard Younger
Messages: 43
Registered: November 2000

Member

Paul van Delst wrote:
>
> Well, my comment was meant to try to get those that swear profusely
> that common blocks are a Bad Thing to explain why. I place common
> blocks in the same category as GOTO statements - if used incorrectly
> they can lead to unbelievably bad source code that may or may not
> work.

Well, the snooty Computer Science answer to this is that common blocks
or global data completely separate the context of the data from its
content. Similarly, with GOTOs, it's easy to separate the context of
one snippet of code from another. When you have a global variable, you
(the indefinite you, which could actually include someone else :-) )
have no real idea what sort of code is using that data. I think the
idea of prohibiting them is to remove the chore and responsibility of
keeping track of the context from anyone else (or any other process of
yours) that wanders along. It's a Good Thing(tm) when the programming
system you use discourages methodologies that tend to cause confusion
and mistakes.

Admittedly, common blocks have some features apart from purely global
data that discourage errors. They have to be specifically invoked, can't
be resized (upwards), and usually IDL projects aren't so big that one
person can't keep track of a set of well controlled commons. The
examples given why commons in IDL specifically are bad seem to involve
doing multiple things at the same time, or with multiple copies of the
same program running.

For myself, I seem to get along nicely without commons. Instead, I
generally use objects, which can carry lots of data implicitly while
still keeping them in context for many routines. The only application I
have thought seriously about using common blocks is a global hardware
lock on some I/O hardware. Even then, I could use a file, since I don't
need to access the lock often. I don't do nearly as much heavy-duty
object graphics (I'm still in line to buy that book when it comes out,
David!) or widgeting as many on this group, though.

Mind you, I'm not supporting banning commons as dogma, but I think there
are enough general objections to them to ask people to think a bit
before they rush out and use them everywhere they can.

Best,
Rich

--
Richard Younger

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[Message index]

		Re: can i place a job advert By: Paul van Delst on Mon, 26 November 2001 09:13
		Re: can i place a job advert By: thompson on Mon, 26 November 2001 08:24
		Re: can i place a job advert By: Paul van Delst on Mon, 26 November 2001 07:22
		Re: can i place a job advert By: Russell Layberry on Mon, 26 November 2001 04:03
		Re: can i place a job advert By: Robert Stockwell on Mon, 26 November 2001 04:48
		Re: can i place a job advert By: Bhautik Joshi on Sun, 25 November 2001 18:29
		Re: can i place a job advert By: Pavel A. Romashkin on Fri, 23 November 2001 12:08
		Re: can i place a job advert By: David Fanning on Fri, 23 November 2001 10:59
		Re: can i place a job advert By: Pavel A. Romashkin on Fri, 23 November 2001 11:22
		Re: Commons, Was: can i place a job advert By: Richard Younger on Mon, 26 November 2001 11:21

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