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Re: Inheritance query [message #17771 is a reply to message #17640]

Thu, 11 November 1999 00:00

m218003
Messages: 56
Registered: August 1999

Member

In article <3829BEB9.A3D2D3A6@astro.cornell.edu>,
"J.D. Smith" <jdsmith@astro.cornell.edu> writes:
>
> One more tip: make good use of the _REF_EXTRA mechanism for chaining up to
> methods which should return something:
>
> pro SubClass::GetProperty,VALUE=val,_REF_EXTRA=e
> val=self.value
> SuperClass::GetProperty,_EXTRA=e
> end
>
> This allows the SuperClass's GetProperty Method to put things into variables for
> return (like properties of the SuperClass, which aren't always just data
> member!), impossible with the _EXTRA mechanism.
>
> JD
>

Thanks JD for bringing this up! I am just experimenting a little bit
with objects myself, and came across this _REF_EXTRA in -- I think it was
Struan's -- code. What I don't understand is: why do you use
_REF_EXTRA in the procedure header but then pass it on to SuperClass
via _EXTRA? I tried to follow the online help on this but couldn't really
find an answer. Is it simply syntax convention that one *always* uses
_EXTRA when calling the routine that accepts _EXTRA or _REF_EXTRA
keywords? Or is there more to it?

Cheers,
Martin

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[Message index]

		Inheritance query By: Bernard Puc on Thu, 04 November 1999 00:00
		Re: Inheritance query By: Struan Gray on Thu, 11 November 1999 00:00
		Re: Inheritance query By: m218003 on Thu, 11 November 1999 00:00
		Re: Inheritance query By: J.D. Smith on Wed, 10 November 1999 00:00
		Re: Inheritance query By: J.D. Smith on Wed, 10 November 1999 00:00
		Re: Inheritance query By: J.D. Smith on Mon, 15 November 1999 00:00

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