Re: Copying objects

["J.D. Smith" <jdsmith(at)astro.cornell.edu>]

James Tappin wrote:
> 
> Is there a "clean" way to make a copy of an object. The best I could do for a
> nice easy case with no pointers or object references in the class was:
> 
> pro Object1::set_all, tstr
> for i = 0, n_tags(tstr)-1 do self.(i) = tstr.(i)
> end
> 
> function Object1::copy
> temp = {object1}
> for i = 0, n_tags(temp)-1 do temp.(i) = self.(i)
> newobj = obj_new('object1')
> newobj -> set_all, temp
> return, newobj
> end
> 
> While it works,  it seems to be a bit of a kludge. Is there a better way?
> 


The easiest way to copy objects in bulk, composited objects and all, is to save
and restore, using:

save,obj,FILENAME=savefile
restore,savefile,RESTORED_OBJECTS=newobj,/RELAXED_STRUCTURE_ASSIGNMENT
newobj=newobj[0]

Don't forget that the object reference variable is also restored, and will
overwrite a variable with the same name in that level (but this can be used to
advantage -- see below).  Also beware of later restoring objects, since their
methods (and those of their superclasses) will be unavailable, and will not be
located automatically.  You can prevent this... see a posting from last year on
restoring objects (I can re-post my resolve_obj if necessary).

Other interesting applications of this method:

Objects which replace themselves from file.  Don't forget to kill the replaced
object:

oldself=self
; Be sure to do some error-catching in here!
restore,file,/RELAXED_STRUCTURE_ASSIGNMENT  ;self is overwritten from file!
;; Do some error catching, but if it worked...
obj_destroy,oldself

and viola! a new self-identity!  Instant "Revert from disk" command.  I use it
all the time.

Another fun and useful technique:  "disconnect" irrelevant portions of objects
before saving them, especially those which will implicitly define structures and
classes that might be changing alot, and which you don't want to keep up with
the method resolution issue.  Simply use pointers, and do something like:

uselesssav=self.UselessStructPtr
self.UselessStructPtr=ptr_new() ; save a null pointer instead!
self->Save
self.UselessStructPtr=uselesssav

etc.  You get the idea.  Be sure to disconnect only those things for which a
null-pointer value isn't disasterous!

Good Luck,

JD

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