[Octave-bug-tracker] [bug #30419] set/get vs setappdata/getappdata for custom properties

[Ben Abbott]

URL:
  <http://savannah.gnu.org/bugs/?30419>

                 Summary: set/get vs setappdata/getappdata for custom
properties
                 Project: GNU Octave
            Submitted by: bpabbott
            Submitted on: Mon 12 Jul 2010 05:09:51 AM EDT
                Category: None
                Severity: 3 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: bpabbott
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Mac OS

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Details:

Matlab doesn't allow users to create new properties for its objects in the
way Octave does. Matlab's "addproperty" serves a different purpose than
Octaves'. The Matlab variant adds a custom property to a COM object, which are
available on Microsoft Windows systems only.

        
http://www.mathworks.com/access/helpdesk/help/techdoc/ref/addproperty.html
        
http://www.mathworks.com/access/helpdesk/help/techdoc/matlab_external/bqdwu3j.html

Instead Matlab uses setappdata(), getappdata(), isappdata() to allow custom
properties to be managed. The first two, work in a manner consistent with
set() and get(), except that they are case sensitive. The latter works as ...

        isappdata = @(h, name) any (strcmp (name, fieldnames (getappdata (h))));

A simple example of this is found in the mechanism by which Matlab manages
the hold state for plots.

>> clf
>> plot (1:10)
>> p = getappdata (gca)

p = 

        PlotColorIndex: 2
    PlotLineStyleIndex: 1

>> hold all
>> p = getappdata (gca)

p = 

        PlotColorIndex: 2
    PlotLineStyleIndex: 1
         PlotHoldStyle: 1

>> hold off
>> p = getappdata (gca)

p = 

        PlotColorIndex: 2
    PlotLineStyleIndex: 1
         PlotHoldStyle: 0

>> hold on
>> p = getappdata (gca)

p = 

        PlotColorIndex: 2
    PlotLineStyleIndex: 1
         PlotHoldStyle: 0

Regarding this example, I'd have responded to the "hold all" discussion but
on the tracker, but was out of email contact.




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