| Re: TEMPORARY (was Re: Fragmented memory with IDL) [message #1037] |
Sat, 22 May 1993 00:22 |
webb
Messages: 3
Registered: May 1993
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Junior Member |
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jdlb@kukui.ifa.hawaii.edu (J-F Pitot de La Beaujardiere) writes:
>
> (deleted description of operation of TEMPORARY)
>
> TEMPORARY, whose effects are PERMANENT, might perhaps be more aptly named
> COPY_AND_DELETE. :^)
>
Actually, TEMPORARY is more like DONOTCOPY_AND_DELETE, since it specifically
does not make a copy of the right hand side.
One somewhat odd but sometimes useful way to use TEMPORARY is to rename
variables. Running
A = TEMPORARY(B)
will effectively rename B to A, without incurring any memory overhead. Why
might you do this? It's one way of making widget applications easier to
write. Suppose you have you favourite widget application on the screen, and
when you click the button you want something to happen to a variable VAR whose
name is unknown to you when you started the widget. Inside the widget event
handler, always operate on, say ACTIONVAR. Make ACTIONVAR a member of a
common block declared within the event handler, then run
ACTIONVAR = TEMPORARY(VAR)
from somewhare else that also declares this common block, and now you can work
on your new variable. In the application I am working on, I keep a bunch of
data sets in named variables, then use a selection widget to swap them in and
out of my ACTIONVAR variable without incurring memory penalties. This keeps
the event handling code simple yet flexible.
Of course, the proper way to do this would be to allow some kind of pointer
type, then all this fooling around would be unecessary. Anybody
else miss pointers? Maybe I assume to much, but it seems that the IDL
interpreter must have pointers to variables readily (or not so readily)
available?
Peter
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