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Re: About keywords and positional parameters [message #32811 is a reply to message #32720]

Thu, 07 November 2002 13:15

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

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

> I agree that you can't tell if a parameter is *meant to be* an input
> parameter, an output parameter, or both without reading the documentation,
> but you certainly can tell whether it is *capable* of passing output:
>
> if arg_present(parameter) then parameter=myungodlyfunction(foo)
>
> ARG_PRESENT() may or many not reveal anything useful, depending on the
> context. Its primary legitimate use is in avoiding calculations of
> optional keyword/argument outputs if the caller didn't ask for them.

I have a feeling this piece of helpful advice is more
likely to confuse Mr. Zhang than enlighten him, but please
don't get me started on the havoc caused by mis-named
functions. Remember, if you want to know if a keyword
is *used* or not in your program, you have to follow
JD's helpful advice:

pro testme, KEY=k
if n_elements(k) ne 0 OR arg_present(k) then $
print,'You used KEY!' else $
print,'You neglected KEY!'
end

You can find all the nitty-gritty details here:

http://www.dfanning.com/tips/keyword_check.html

Cheers,

David

--
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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