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Re: Copying an object [message #17023 is a reply to message #17008]

Tue, 31 August 1999 00:00

davidf
Messages: 2866
Registered: September 1996

Senior Member

Pavel Romashkin (promashkin@cmdl.noaa.gov) writes:

> Since object structures are heap variables, couldn't a wizard like David or
> Liam hack a small piece of code to allow unauthorized access to object
> structures directly through pointers? Something like
> a = ptr_valid(Obj_heap_var_number, /cast) ? This would be dangerous but
> probably useful because then duplication would be a one liner.

Well, probably Liam can, but I'm left scratching my head over
what seem to me to be insurmountable problems. Randy Frank,
who wrote much of this object code when he was at RSI,
has sent me a private e-mail outlining even more problems
than I was aware of on my own. For example, he points
out that many times the model objects (which is what
we were discussing earlier this morning) have parents.
What should be done about those? Should the copy have
the *same* parents, or any parents? What implications
does this have if the parents are destroyed or changed
in some way? You would have to answer this question
for yourself. It is unlikely that a general algorithm
could be written.

Of course, if the GetProperties and SetProperties methods
of the object are well written, you could simply do something
like this:

copyObj = Obj_New('OurObjectClass')
oldObj->GetProperty, All=allSettableProperties
copyObj->SetProperty, _Extra=allSettableProperties

But in practical applications (at least the ones I've
written) this doesn't always work.

You can also try SAVEing and RESTOREing your objects,
but this has the problem that sometimes the methods of
restored objects can't be found. (See JD Smith's comments
on this on my web page.)

And yet, I find that I need a copy of the object quite
often. I haven't found a perfect solution yet, but something
like the solution outlined on my web page is where I usually
start from. So far, I've been able to hack my way around
some kind of solution in every case.

Cheers,

David

P.S. Let's just say if Liam *can* write something, I'd be
very interested in seeing it. :-)

--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Re: Copying an object By: davidf on Thu, 02 September 1999 00:00
		Re: Copying an object By: Nick Bower on Thu, 02 September 1999 00:00
		Re: Copying an object By: steinhh on Wed, 01 September 1999 00:00
		Re: Copying an object By: Mark Hadfield on Wed, 01 September 1999 00:00
		Re: Copying an object By: Mark Hadfield on Wed, 01 September 1999 00:00
		Re: Copying an object By: Mark Hadfield on Wed, 01 September 1999 00:00
		Re: Copying an object By: davidf on Tue, 31 August 1999 00:00
		Re: Copying an object By: Liam Gumley on Tue, 31 August 1999 00:00
		Re: Copying an object By: davidf on Tue, 31 August 1999 00:00
		Re: Copying an object By: davidf on Tue, 31 August 1999 00:00

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