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Re: Optional parameters [message #38182 is a reply to message #38174]

Tue, 24 February 2004 21:50

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

JD Smith <jdsmith@as.arizona.edu> writes:
> I'd offer another real life example where read-write keyword variables
> can get you into trouble. When you call a function several times in a
> row, expecting the same results each time, but in actuality the
> keyword variable is defined after the first invocation, which can
> change the function's behavior:
>
> a=myfunc(test,FUNNY_VARIABLE=foo) ; foo undefined
> a=myfunc(test,FUNNY_VARIABLE=foo) ; foo defined
> a=myfunc(test,FUNNY_VARIABLE=foo) ; foo defined

Yes, I've encountered this kind of problem before as well, and it's
one of the most evil and difficult problems to solve.

That's why I define all of my functions as

pro myfunc, value=value0

;; Default value ...
if n_elements(value0) EQ 0 then value = 1 $
;; ... or requested value
else value = round(value0(0))
...
end

The "0" variable is the pristine variable that never gets changed, and
the regular variable is the one that is internal to the procedure. I
do that as a matter of habit now and it's not too labor intensive.

I do kind of wish that there would be an automatic way for IDL to peel
off a local copy of a variable for internal calculations.

Craig

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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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[Message index]

		Re: Optional parameters By: Pavel Romashkin on Wed, 25 February 2004 10:21
		Re: Optional parameters By: David Fanning on Wed, 25 February 2004 09:26
		Re: Optional parameters By: Craig Markwardt on Wed, 25 February 2004 08:48
		Re: Optional parameters By: David Fanning on Wed, 25 February 2004 07:08
		Re: Optional parameters By: Paul Van Delst[1] on Wed, 25 February 2004 06:49
		Re: Optional parameters By: Craig Markwardt on Tue, 24 February 2004 21:50
		Re: Optional parameters By: JD Smith on Tue, 24 February 2004 14:03
		Re: Optional parameters By: R.G. Stockwell on Tue, 24 February 2004 14:02
		Re: Optional parameters By: Pavel Romashkin on Tue, 24 February 2004 13:45
		Re: Optional parameters By: JD Smith on Tue, 24 February 2004 12:13
		Re: Optional parameters By: Pavel Romashkin on Tue, 24 February 2004 09:59
		Re: Optional parameters By: David Fanning on Tue, 24 February 2004 09:08
		Re: Optional parameters By: David Fanning on Tue, 24 February 2004 08:31
		Re: Optional parameters By: JD Smith on Tue, 24 February 2004 08:10
		Re: Optional parameters By: David Fanning on Mon, 23 February 2004 17:39
		Re: Optional parameters By: David Fanning on Mon, 23 February 2004 17:05

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