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Re: renaming a variable without making a copy [message #68924 is a reply to message #68923]

Tue, 08 December 2009 13:51

Kenneth P. Bowman
Messages: 585
Registered: May 2000

Senior Member

In article <MPG.2587fff16b170da398968a@news.giganews.com>,
David Fanning <news@dfanning.com> wrote:

> newName = Temporary(oldName)

Can anyone explain to me what TEMPORARY actually does? The documentation
says

The TEMPORARY function returns a temporary copy of a variable, and sets
the original variable to "undefined".

which makes no sense to me at all. Doesn't making a "temporary copy
of a variable" occupy memory? Perhaps I am confused by the use of the name
"TEMPORARY".

My concept of an IDL variable (which could easily be wrong) is: some
metadata that describes the variable (what you get with the SIZE function)
and the actual data that comprises the variable. These things could be
in different places in memory, and the metadata could contain, for example,
a pointer to the actual data. Most of the time, I don't need to know.

Does TEMPORARY wipe out the old metadata (replacing it with
"undefined") and create new "unnamed" metadata that points to the data part
of the destroyed variable?

The example in the Docs is not very revealing.

Why does

A = TEMPORARY(A) + 1

use less memory than

A = A + 1

??

I suppose there is a good reason that the latter example "creates a new
array for the result of the addition, places the sum into the new array,
assigns it to A, and then frees the old allocation of A", although it
just seems to me like the interpreter is being obtuse.

Cheers, Ken

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[Message index]

		Re: renaming a variable without making a copy By: David Fanning on Wed, 09 December 2009 05:19
		Re: renaming a variable without making a copy By: lecacheux.alain on Wed, 09 December 2009 01:42
		Re: renaming a variable without making a copy By: David Fanning on Tue, 08 December 2009 14:39
		Re: renaming a variable without making a copy By: Michael Galloy on Tue, 08 December 2009 14:39
		Re: renaming a variable without making a copy By: Kenneth P. Bowman on Tue, 08 December 2009 13:51
		Re: renaming a variable without making a copy By: David Higgins on Tue, 08 December 2009 06:51
		Re: renaming a variable without making a copy By: David Fanning on Tue, 08 December 2009 05:18
		Re: renaming a variable without making a copy By: Kenneth P. Bowman on Wed, 09 December 2009 07:02
		Re: renaming a variable without making a copy By: R.Bauer on Wed, 09 December 2009 09:06
		Re: renaming a variable without making a copy By: lecacheux.alain on Wed, 09 December 2009 06:33

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