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Re: Optional parameters [message #38199 is a reply to message #38198]

Tue, 24 February 2004 08:10

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Mon, 23 Feb 2004 18:05:20 -0700, David Fanning wrote:

> Michael Wallace writes:
>
>> The learning of IDL continues.... today's question is about optional
>> parameters. Specifically, how do you make a parameter optional? I can
>> find stuff in the IDL documentation regarding position parameters and
>> keywords, but I haven't found anything yet about optional parameters.
>> So, how do you create optional parameters and what are common gotchas
>> with using them?
>
> An optional parameter can be either a positional parameter or a keyword
> parameter, although the general rule of thumb is that positional
> parameters are always required and keyword parameters are always
> optional. The rule is broken frequently, especially with positional
> parameters and less so with keyword parameters (having to suffer
> the wrath of Coyote if you violate the "keyword is optional" dictum
> probably accounts for the decreased frequency of the latter).
>

I would have put it more simply: all parameters, keyword or
positional, are optional in IDL. How you choose to treat missing
parameters defines the behavior of a routine. See David's linked
article for more. I think there are enough useful example (even among
RSI's own offerings) which violate this general rule of thumb that it
shouldn't be considered a rule.

JD

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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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