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Re: Pass-By-Reference question. [message #38484 is a reply to message #38470]

Thu, 11 March 2004 04:40

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Timm Weitkamp writes:

> Here's an observation that makes it even stranger: when you change
> "whaddup.pro" so that NODATA is explicitly set to 0 (instead of one)
> inside the routine, and you then try to override that by calling
>
> IDL> whaddup, nodata=1
>
> The amazing thing is that this way it works (i.e., inherited overrides
> explicit keyword).

I discovered this yesterday when I was playing around with
the problem. It reminds me of what happens sometimes when
you incorrectly use KEYWORD_SET instead of N_ELEMENTS to
determine if a keyword is defined or not, and set a
default value. For example, if you use this expression:

IF Keyword_Set(mykeyword) THEN mykeyword = 3

instead of this expression:

IF N_ELements(mykeyword) EQ 0 THEN mykeyword = 3

then it is impossible to set this keyword to 0. I just
haven't been able to come up with a specific mechanism
for this particular situation. But I *have* seen RSI
programmers make this kind of mistake in code, so I think
the theory is plausible.

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		Re: Pass-By-Reference question. By: Mark Hadfield on Thu, 11 March 2004 12:07
		Re: Pass-By-Reference question. By: David Fanning on Thu, 11 March 2004 04:40
		Re: Pass-By-Reference question. By: Chris Lee on Thu, 11 March 2004 02:12
		Re: Pass-By-Reference question. By: Timm Weitkamp on Thu, 11 March 2004 01:28
		Re: Pass-By-Reference question. By: David Fanning on Wed, 10 March 2004 20:34
		Re: Pass-By-Reference question. By: Mark Hadfield on Wed, 10 March 2004 20:24
		Re: Pass-By-Reference question. By: timrobishaw on Wed, 10 March 2004 19:04
		Re: Pass-By-Reference question. By: Mark Hadfield on Wed, 10 March 2004 15:55
		Re: Pass-By-Reference question. By: timrobishaw on Wed, 10 March 2004 15:34
		Re: Pass-By-Reference question. By: Craig Markwardt on Wed, 10 March 2004 13:24
		Re: Pass-By-Reference question. By: Mark Hadfield on Wed, 10 March 2004 12:13
		Re: Pass-By-Reference question. By: Chris Lee on Wed, 10 March 2004 01:37
		Pass-By-Reference question. (ARG_PRESENT) By: Andry William (Please on Fri, 12 March 2004 11:52
		Re: Pass-By-Reference question. By: Craig Markwardt on Thu, 11 March 2004 17:37

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