| Treating an object as a structure [message #65432] |
Wed, 04 March 2009 12:20  |
natha
Messages: 482
Registered: October 2007
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Senior Member |
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If I've a struct I can do something like that:
a={s:'string', l: 0l}
print, n_tags(a)
print, tag_names(a)
help, a, /str
etc.
But if I've an object I can't do the same... Is it possible to parse
all the attributes inside the object using something similar ?
I mean, I don't want to use the GetProperty method, I only want to
know which attributes are stored in the definition of the object.
pro object__define
str ={ object, $
attribute_s: '', $
attribute_l: 0l }
end
The object saves a struct. It could be possible to take information
about this without the use of the getproperty method.
thanks
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| Re: Treating an object as a structure [message #65487 is a reply to message #65432] |
Fri, 06 March 2009 14:36  |
JDS
Messages: 94
Registered: March 2009
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Member |
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I use this technique a lot:
snapshot=create_struct(NAME=obj_class(self))
or simply
snapshot={MYCLASS}
struct_assign,self,snapshot
later apply snapshot:
struct_assign,snapshot,self
This allows me to make snapshots of object data for the purpose of
undoing changes, or examining how it was at a certain point in time.
Keep a pointer to a list of these, and you have multiple undo. Add a
text phrase when snapshotting ("Frobnoid change") and you can
advertise "Undo Forbnoid change" and so on.
The lack of garbage collection starts getting painful at this point
though (since older versions could refer to data newer versions have
deleted).
Remember that snapshots of heap pointers (at whatever level in the
heirarchy) are not immutable. If you want a deep copy, you can use
the save/restore trick, first calling the new HEAP_NOSAVE routine on
items you won't need a deep copy of. Or you can simply replicate
certain heap data by hand (new=ptr_new(*old)). This reminds me that
we're still lacking deep copy capability without hitting the disk.
JD
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| Re: Treating an object as a structure [message #65508 is a reply to message #65432] |
Thu, 05 March 2009 08:01 |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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llo wrote:
> On Mar 4, 4:59 pm, David Fanning <n...@dfanning.com> wrote:
>> llo writes:
>>> It works but the problem is that the struct is not the object itself.
>> No, that's pretty much the point of objects. :-)
>
> That's not true David. You can get all the object attributes doing
> this:
>
> a=OBJ_NEW('object')
> str=CREATE_STRUCT(NAME=OBJ_CLASS(a))
> STRUCT_ASSIGN, a, str
>
> Now, ypu have all the attributes of a in the struct str.
>
> Cheers,
>
> Bernat
>
>
Not so fast! That trick only works inside an object's methods:
IDL> a=OBJ_NEW('idlgrmodel')
IDL> str=CREATE_STRUCT(NAME=OBJ_CLASS(a))
IDL> STRUCT_ASSIGN, a, str
% STRUCT_ASSIGN: Object instance data is not visible outside class
methods: A
% Execution halted at: $MAIN$
Mike
--
www.michaelgalloy.com
Associate Research Scientist
Tech-X Corporation
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| Re: Treating an object as a structure [message #65514 is a reply to message #65432] |
Wed, 04 March 2009 16:52 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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llo writes:
> Lately, we've learned a lot with my questions.
Yes, but be careful. Karma is a funny thing, and
if you learn too much you will be made to
listen to other people ask clever questions that
you can only hope to answer. ;-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Treating an object as a structure [message #65518 is a reply to message #65432] |
Wed, 04 March 2009 15:54 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Michael Galloy writes:
> Just use STRUCT_ASSIGN:
Well, shoot, I knew that! How come I couldn't remember it? :-(
Probably because I didn't write it down on my web page,
my (almost) guaranteed way of remembering these sorts of
things. Look for an article soon. ;-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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