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Re: About keywords and positional parameters [message #32790 is a reply to message #32720]

Fri, 08 November 2002 12:32

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

JD Smith (jdsmith@as.arizona.edu) writes:

> Just to be clear, I've never actually used this method (using
> arg_present() essentially as an input test) in real-life code... it's
> not really all that helpful. In fact, I wrote it just to get under
> your skin, what with your braggadocious claim that you could never
> know if a keyword is *used* ;). From my perspective, there are only
> three real cases worth keeping track of:
>
> 1. An input keyword: Use n_elements() to see if it's present, or
> keyword_set() if it's intended to be a boolean.
> 2. An output keyword: Use arg_present() if computing the output is
> actually optional in your program, and you want to save the
> trouble of calculating it if the caller didn't ask for it.
> 3. An input/output keyword: Use a combination of the above two,
> reserving n_elements/keyword_set for input tests, and arg_present
> for output tests.

JD and I don't really need to be having this
conversation, because both of us know perfectly
well how to handle keywords correctly (and neither of
us would probably ever have a need to know if a keyword
was "used" or not). But for the sake of completeness, and
for the edification of the 63.58% of IDL programmers
(according to an informal survey I've taken) that use
KEYWORD_SET incorrectly in their programs, I reiterate:
KEYWORD_SET [capitals deliberate] should be used ONLY
for keywords that have Boolean values. :-)

Cheers,

David

P.S. Let's just say that if everyone ripped KEYWORD_SET
out of their code and substituted N_ELEMENTS the world
would probably be a better place. (Or, at the very least,
more functional.)

--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		About keywords and positional parameters By: fengliza on Thu, 07 November 2002 08:15
		Re: About keywords and positional parameters By: David Fanning on Fri, 08 November 2002 12:32
		Re: About keywords and positional parameters By: JD Smith on Fri, 08 November 2002 11:45
		Re: About keywords and positional parameters By: David Fanning on Thu, 07 November 2002 13:15
		Re: About keywords and positional parameters By: JD Smith on Thu, 07 November 2002 12:37
		Re: About keywords and positional parameters By: R.G. Stockwell on Thu, 07 November 2002 10:26
		Re: About keywords and positional parameters By: David Fanning on Thu, 07 November 2002 08:57

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