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Re: IDL Shapefile Object [message #28294 is a reply to message #28292]

Thu, 29 November 2001 17:26

Mark Hadfield
Messages: 783
Registered: May 1995

Senior Member

From: "David Fanning" <david@dfanning.com>
> Suppose one of the fields for the object was a
> pointer to some image data. The same image pointer
> might be present in several objects (to save
> copying the huge image). Any decent object cleanup
> routine would certainly free the pointer, but maybe
> you don't want it destroyed because then the other
> objects that are using it wouldn't work properly.
>
> In this case a HANG_ON_DONT_DO_IT keyword
> on the cleanup method might be appropriate.

I have run into this situation and when I did (in my ignorance) I added a
HANG_ON_DONT_DESTROY_THE_DATA keyword to the Init method and a corresponding
tag in the class structure. Then in the cleanup method:

if not self.hang_on_dont_destroy_the_data then $
ptr_free, thedata

If I had to justify doing it this way I would say that destruction of
objects is often carried out by code that doesn't know much about the
object's properties, and this is less true of object-creation code.

---
Mark Hadfield
m.hadfield@niwa.cri.nz http://katipo.niwa.cri.nz/~hadfield
National Institute for Water and Atmospheric Research

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[Message index]

		Re: IDL Shapefile Object By: Kelly Dean on Fri, 30 November 2001 11:52
		Re: IDL Shapefile Object By: alt on Thu, 29 November 2001 19:29
		Re: IDL Shapefile Object By: Mark Hadfield on Thu, 29 November 2001 17:26
		Re: IDL Shapefile Object By: David Fanning on Thu, 29 November 2001 16:40
		Re: IDL Shapefile Object By: Mark Hadfield on Thu, 29 November 2001 15:47
		Re: IDL Shapefile Object By: David Fanning on Thu, 29 November 2001 14:31
		Re: IDL Shapefile Object By: David Fanning on Thu, 29 November 2001 13:26
		Re: IDL Shapefile Object By: mvukovic on Mon, 03 December 2001 07:15

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