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Re: keyword_set bug or feature [message #4229 is a reply to message #4216]

Fri, 12 May 1995 00:00

sterner
Messages: 106
Registered: February 1991

Senior Member

phil@peace.med.ohio-state.edu (Phil) writes:

> I just can across another 'feature' and was wondering if others felt
> that it is really a 'bug' or if there is some way to over come it. It
> has to do with keywords in functions or procedures. I use several and
> check to see if the are set using

> IF NOT(keyowrd_set(key)) THEN BEGIN
> ;set a default value here
> ENDIF

> The problem comes in if the user wants to set key = 0. If so then it
> appears to the above test that the keyword is not set even though in
> the function call the user typed
>
> Result = somefunction(var,key=0)

> What gives? Can I just add key = key + 1 and key = key - 1 around the
> testing if statement?

I always use a statement like the following:

if n_elements(key) eq 0 then key=default_value

This is not something you would guess as the obvious solution
but n_elements returns 0 if its argument is undefined. You only
need a default value when your keyword is undefined so this works.
It also works the same for ordinary positional arguments.

What is missing is a way to determine if an output keyword was
requested in the call. Often the variable in such a keyword is
undefined since it is an output of the routine. I don't know
anyway to find out if the caller actually requested the output keyword
or not so any such keywords must always be set. Occasionally it
may take a lot of processing to find the desired output. It would be
nice if you could determine if it was really requested and only do it
then.

Ray Sterner sterner@tesla.jhuapl.edu
The Johns Hopkins University North latitude 39.16 degrees.
Applied Physics Laboratory West longitude 76.90 degrees.
Laurel, MD 20723-6099
WWW Home page: ftp://fermi.jhuapl.edu/www/s1r/people/res/res.html

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[Message index]

		keyword_set bug or feature By: phil on Fri, 12 May 1995 00:00
		Re: keyword_set bug or feature By: zawodny on Fri, 12 May 1995 00:00
		Re: keyword_set bug or feature By: zawodny on Fri, 12 May 1995 00:00
		Re: keyword_set bug or feature By: wmc on Fri, 12 May 1995 00:00
		Re: keyword_set bug or feature By: thompson on Fri, 12 May 1995 00:00
		Re: keyword_set bug or feature By: llobet on Fri, 12 May 1995 00:00
		Re: keyword_set bug or feature By: sterner on Fri, 12 May 1995 00:00
		Re: keyword_set bug or feature By: thompson on Tue, 16 May 1995 00:00
		Re: keyword_set bug or feature By: soc on Tue, 16 May 1995 00:00
		Re: keyword_set bug or feature By: thompson on Thu, 25 May 1995 00:00

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