A problem in MATLAB OOP documentation

In MATLAB R2014b OOP documentation in page '10-33' we have some codes about 'Supporting Both Handle and Value Subclasses'. You can see the codes here:

classdef (HandleCompatible) Utility
    methods
        function obj = resetDefaults(obj)
            % Reset properties to default and return object
            mc = metaclass(obj); % Get meta.class object
            mp = mc.PropertyList; % Get meta.property objects
            for k=1:length(mp)
                % For each property, if there is a default defined,
                % set the property to that value
                if mp(k).HasDefault && ~strcmp(mp(k).SetAccess,'private')
                    obj.(mp(k).Name) = mp(k).DefaultValue;

                  end
              end
          end
      end
  end

classdef PropertyDefaults < Utility
    properties
        p1 = datestr(rem(now,1)); % Current time
        p2 = 'red'; % Character string
        p3 = pi/2; % Result of division operation
    end
end

Now we insert this :

pd = PropertyDefaults with properties:
p1: ' 4:54 PM'
p2: 'red'
p3: 1.5708

Assign new values that are different from the default values:

pd.p1 = datestr(rem(now,1));
pd.p2 = 'green';
pd.p3 = pi/4;

All pd object property values now contain values that are different from the default values originally defined by the class:

pd =
PropertyDefaults with properties:

p1: ' 5:36 PM'
p2: 'green'
p3: 0.7854

Call the resetDefaults method, which is inherited from the Utility class. Because the PropertyDefaults class is not a handle class, you must return the modified object for reassignment in the calling function's workspace.

pd = pd.resetDefaults
pd =
PropertyDefaults with properties:
p1: ' 4:54 PM'
p2: 'red'
p3: 1.5708

This part of Object-oriented programming documentation is about using 'HandleCompatible' class attribute but when we remove this attribute from Utility class we have same behavior!! what is purpose of this attribute? I'm using MATLAB R2014b.

Thanks.

Answer 1

[Geoff Hayes]

Jack - I think that the purpose of this attribute (if set to true) is to allow handle subclasses derived from Utility to be compatible with that base class. In the above example, the derived class PropertyDefaults is a Value class (like its parent Utility), so removing the HandleCompatible would have no effect.

Suppose then that we derive another class (based on the examples from the Supporting Both Handle and Value Subclasses) that is a handle class

 classdef PropertyDefaultsHandle < Utility & handle
   properties
      p1 = datestr(rem(now,1)); % Some time
      p2 = 'blue';              % Character string
      p3 = 42.4242/2;           % Result of division operation
   end
 end

Now, if you instantiate the class as

 pd = PropertyDefaultsHandle

and follow through with

 pd.p1 = datestr(rem(now,1));
 pd.p2 = 'green';
 pd.p3 = pi/4;

you can reset to the defaults simply (without the assignment seen in the previous example) as

 pd.resetDefaults

and pd is back to its default self. This example demonstrates how the attribute (when set to true) can allow handle and value subclasses to be derived from the same base value class.

[Jack]

Thank you for answer Geoff.