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Re: reverse problem [message #46178 is a reply to message #46053]

Fri, 04 November 2005 09:22

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

R.G. Stockwell writes:

> As Paolo points out, the routine is returning the keyword value,
> replicated to the size of the input array. Neat!
> So, it is treating reverse as a single element array, then accessing
> it with the input array as an index (which exceeds the "reverse" array
> size, and by IDL's default rule, it replicates the last number).
>
> example:
> IDL> x = 1
>
> IDL> print, x(findgen(10))
>
> 1 1 1 1 1 1 1 1 1 1
>
>
> But the really really strange thing is that, as I showed in my original
> post,
> that the problem was persistent. After running the routine, the keyword
> "reverse"
> escaped the local scope of the routine, and came to main level (and thus
> overwriting the
> reverse function at the main level). Of course, this is how keywords are
> supposed to work,
> but it was kind of a surprise.

Oh, this is neat! This is now my favorite example
in my Pass-by_Reference, Pass-by-Value lecture. :-)

Cheers,

David

P.S. By the way, putting Compile_Opt idl2 in your IDL startup
file goes a LONG way to sorting out a lot of these kinds of
problem.
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		reverse problem By: news.qwest.net on Thu, 03 November 2005 16:24
		Re: reverse problem By: David Fanning on Fri, 04 November 2005 14:31
		Re: reverse problem By: savoie on Fri, 04 November 2005 14:03
		Re: reverse problem By: news.qwest.net on Fri, 04 November 2005 13:16
		Re: reverse problem By: David Fanning on Fri, 04 November 2005 12:27
		Re: reverse problem By: news.qwest.net on Fri, 04 November 2005 10:42
		Re: reverse problem By: David Fanning on Fri, 04 November 2005 09:22
		Re: reverse problem By: news.qwest.net on Fri, 04 November 2005 09:04
		Re: reverse problem By: MarioIncandenza on Fri, 04 November 2005 08:59
		Re: reverse problem By: Paolo Grigis on Fri, 04 November 2005 08:25
		Re: reverse problem By: liamgumley on Fri, 04 November 2005 07:41
		Re: reverse problem By: news.qwest.net on Fri, 04 November 2005 07:38

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