comp.lang.idl-pvwave archive: archive » Re: _extra and call

Home » Public Forums » archive » Re: _extra and call_method

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: _extra and call_method [message #42338 is a reply to message #42337]

Mon, 31 January 2005 06:41

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Ben Tupper writes:

> I'm running on just one cup of coffee this morning so maybe this is a fuzzy
> question: could you explain the circumstances in which this is useful? If you
> return dummy named structure - well, what about all the work that goes into
> populating its properties it via the INIT function? Or is this for simple data
> structures (ala widget event structures, etc. ?)

Since objects are implemented as named structures in IDL,
I seem to find a number of instances where it would be
helpful to know what the names of the fields in that object
structure are. For example, one of the hugely time-consuming
tasks in object writing is creating the GetProperty and SetProperty
methods that allow you to manipulate and set/get values in the
object structure. Wouldn't it be nice to automate those tasks
and be able to get and set any property (field) in the object
without necessarily knowing ahead of time what those properties
might be? For example, I might like to respond to this:

anObject -> SetProperty, Foo=5

Without specifically having to define the FOO keyword for the object.

If FOO were a field of this object, I could write a generic SetProperty
method like this (I'm leaving out a couple of important details, but I
plan an article soon):

PRO myObject::SetProperty, _Extra=extra

; What keywords are you looking for?
keywords = Tag_Names(_extra)

; What properties (fields) can be changed?
Call_Procedure, Obj_Class(self) + '__define', struct ;**************
properties = Tag_Names(struct)

; Set the value of each field according to the keyword value.
FOR j=0,N_Elements(keywords)-1 DO
propertyIndex = Where(StrPos(properties, keywords[j]) EQ 0, match)
IF match EQ 1 THEN self.(propertyIndex) = _extra.(j)
ENDFOR

END

I can do something similar for a GetProperty method. Adding (copying,
really) these two generic methods to every object I create, is MUCH
less time consuming than defining each and every keyword for each
and every property I hope to change.

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/

Report message to a moderator

[Message index]

		Re: _extra and call_method By: David Fanning on Tue, 01 February 2005 07:40
		Re: _extra and call_method By: btt on Tue, 01 February 2005 07:18
		Re: _extra and call_method By: btt on Mon, 31 January 2005 07:43
		Re: _extra and call_method By: David Fanning on Mon, 31 January 2005 06:41
		Re: _extra and call_method By: btt on Mon, 31 January 2005 05:13
		Re: _extra and call_method By: David Fanning on Fri, 28 January 2005 14:21
		Re: _extra and call_method By: Benjamin Hornberger on Fri, 28 January 2005 12:38
		Re: _extra and call_method By: David Fanning on Thu, 27 January 2005 17:00

Previous Topic:	Re: Aggregating an array
Next Topic:	Color behavior when using TEXTURE MAP

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sat Nov 29 05:35:22 PST 2025

Total time taken to generate the page: 0.72230 seconds