Strange handle behavior (was Re: [Changeset]: Re: cla() ?)

[Ben Abbott]

On Oct 7, 2008, at 5:43 PM, Ben Abbott wrote:

>
> On Oct 7, 2008, at 9:10 AM, Michael Goffioul wrote:
>
>> While we're talking about __go_delete__, does anybody
>> remember what was the idea behind removing an object
>> from its parent's children in __go_delete__, instead of
>> gh_manager::free? This makes life slighlty more complex
>> if you want to delete an object from C++, where you would
>> typically use gh_manager::free, but you then have to remove
>> the child manually from its parent's children.
>>
>> I don't think I wrote that part of the code, and I can't figure
>> out why it is written that way.
>>
>> Michael.
>
> MIght what describe be responsible for why the code below does not  
> return the axis limits to its default values?
>
> octave:21> figure(1)
> octave:22> clf
> octave:23> axis
> ans =
>
>   0   1   0   1   0   1
>
> octave:24> plot(1:10)
> octave:25> text(5,5,'some text')
> octave:26> axis
> ans =
>
>    0   10    0   10   -1    1
>
> octave:27> delete (get(gca,'children'))
> octave:28> axis auto
> octave:29> axis
> ans =
>
>    0   10    0   10   -1    1
>

Some more strange behavior. I wrote a trivial script called  
"test_delete.m", which contains the lines below.

----------------------
clear all
figure (1)
clf
plot (1:10)
hc = get (gca, 'children');
delete (hc)
axis auto
p = get (hc)
----------------------

When I run it I get ...

octave:30> test_delete
error: get: invalid handle (= -6.17358)
error: called from:
error:   /Users/bpabbott/Development/Octave Toolbox/cla/test_cla.m at  
line -1, column -1

With the exception of the x/y limits not changing, everything looks  
ok. However, if I then manually type the last line ...

octave:30> p = get(hc)
p =
{
   beingdeleted = off
   busyaction = queue
   buttondownfcn = [](0x0)
   children = [](0x0)
   clipping = on
   createfcn = [](0x0)
   deletefcn = [](0x0)
   handlevisibility = on
   hittest = on
   interruptible = on
   parent = -7.3210
   selected = off
   selectionhighlight = on
   tag =
   type = text
   userdata = [](0x0)
   visible = on
   __modified__ = on
   uicontextmenu = [](0x0)
   string =
   units = data
   position =

      0   0   0

   rotation = 0
   horizontalalignment = left
   color =

      0   0   0

   fontname = Helvetica
   fontsize =  10
   fontangle = normal
   fontweight = normal
   interpreter = tex
   backgroundcolor = none
   displayname =
   edgecolor = none
   erasemode = normal
   editing = off
   fontunits = points
   linestyle = -
   linewidth =  0.50000
   margin =  1
   verticalalignment = middle
}

If I manually type each line then all appears to work as expected.

I have no idea what is happening here, but thought the example might  
help someone else track down the problem.

Ben