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Re: keyword_set bug or feature [message #4227 is a reply to message #4216]

Fri, 12 May 1995 00:00

thompson
Messages: 584
Registered: August 1991

Senior Member

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

> Thanks to those who responded to my ? concerning common blocks.

> 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?

This is a very common error that people make. They want to use KEYWORD_SET()
to test for the *existence* of keyword variables. KEYWORD_SET() is *only* for
keywords which can take True or False values, and has the (quite correct in my
opinion) property that not passing something is the same as passing it as
False.

To test for the *existence* of keywords that can take arbitrary values, use the
function N_ELEMENTS() instead.

Bill Thompson

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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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