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Re: IDL objects and names [message #34066 is a reply to message #33970]

Wed, 12 February 2003 07:09

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Sebastian (s@visita2.die.upm.es) writes:

> that lostObject thing is cool, made me re-read the OBJ_VALID docs....
> Now I am of course a little bit lazy and don't want to write a PrintName
> procedure for each object type I am using.
> Is there something like an IDLClass that all IDLgr* classes inherit from?
> I know that the reference manual says for most of the IDLgr* classes "This
> class has no superclasses", but is it true? I mean, what's the point of
> having "objects" and making no use of their (theoretical) capabilities?

No, I'm afraid it is true. One of the huge disadvantages of
IDL objects is that they are based on named structures, which
means the field names in the structure can't be duplicated.
In practice, this makes it hard to have deep inheritance
hierarchies. But what is even worse, is it makes it extremely
difficult to have multiple inheritance hierarchies.

So, for example, if IDLgrSurface and IDLgrAxis both inherited,
say, IDLgrBasicThing, then I could not make an IDLgrPlot object
that inherited both IDLgrSurface and IDLgrAxis because the
IDLgrBasicThing structure would be added to the definition
twice. It is a very difficult limitation to get around, especially
with large object programs. I think this is one of the reasons
we haven't seen RSI offer much in the way of higher level
object graphics functionality yet.

Cheers,

David

--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@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]

		IDL objects and names By: s[1] on Wed, 12 February 2003 03:32
		Re: IDL objects and names By: David Fanning on Wed, 12 February 2003 17:36
		Re: IDL objects and names By: Rick Towler on Wed, 12 February 2003 14:17
		Re: IDL objects and names By: dick on Wed, 12 February 2003 13:47
		Re: IDL objects and names By: David Fanning on Wed, 12 February 2003 13:38
		Re: IDL objects and names By: Rick Towler on Wed, 12 February 2003 12:50
		Re: IDL objects and names By: Pavel A. Romashkin on Wed, 12 February 2003 10:38
		Re: IDL objects and names By: Randall Skelton on Wed, 12 February 2003 08:42
		Re: IDL objects and names By: David Fanning on Wed, 12 February 2003 07:16
		Re: IDL objects and names By: David Fanning on Wed, 12 February 2003 07:09
		Re: IDL objects and names By: s[1] on Wed, 12 February 2003 06:37
		Re: IDL objects and names By: David Fanning on Wed, 12 February 2003 05:33

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