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Re: About keywords and positional parameters [message #32812 is a reply to message #32720]

Thu, 07 November 2002 12:37

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Thu, 07 Nov 2002 09:57:54 -0700, David Fanning wrote:

> lily_zhang (fengliza@sina.com) writes:
>
>> Would you tell me how to distinguish the keywords and positional
>> parameters in IDL procedures and functions?
>
> Positional parameters are those variables that come after the command
> name. They have a position after the name (1, 2, 3, etc.). Keyword
> parameters also come after the command name, but they have a
> KEYWORD=variable (or sometimes a /KEYWORD, which means KEYWORD=1)
> appearance. Keyword parameters can come in any order and don't affect
> the count of positional parameters.
>
> You can't tell from looking whether a positional or keyword parameter is
> an input parameter or an output parameter (or both). You have to read
> the documentation to discover this.
>
>
>
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.

JD

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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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