MATLAB: How to hide away properties of an object

classobjectsooppcode

I have a class in Matlab, which has a number of properties. I want to make a pcode to obfuscate content of the class. But I couldn't find any way to hide properties of the class: using struct(obj) all the properties become available. Is there any workaround?

Best Answer

I don't think there's any way to hide private properties from struct.

The only workaround I could think of would be to store the private properties in another class (handle) and use a persistent containers.Map in a function to access that class. Would be a bit of a hassle, so you need to really want to hide these properties:

classdef ClassWithPropertiesToHide
   properties  (Access = public)   %properties that are public, hence don't need hiding
      something;
   end
   properties  (Access = private)
      objectID;    %will be visible through struct, but useless. Used as key in the container.Maps which unfortunately can't use a class as a key
   end
   methods (Access = public)
      function this = ClassWithPropertiesToHide()
         persistent idcount;  %unique id for each class instance to be used as key in the map
         if isempty(idcount)
            idcount = 0;
         else
            idcount = idcount + 1;
         end
         this.objectID = idcount;
         privateprops = GetPrivateProperties(this);   %privateprops is a handle class, so can be modified here
         privateprops.someprop = somevalue;
         privateprops.someotherprop = someothervalue;
      end
      function someotherfunction(this)
          privateprops = GetPrivateProperties(this);  %get private properties
          %do something
      end
   end
   methods (Access = private)
      function privateprops = GetPrivateProperties(this)
         persistent propcontainer;
         if isempty(propcontainer)
            propcontainer = containers.Map;
         end
         if ~isKey(propcontainer, this.objectID)
            propcontainer(this.objectID) = PrivatePropertiesClass  %PrivatePropertiesClass is the class to hold the private properties. Its properties have to be public
         end
         privateprops = propcontainer(this.objectID);
      end
   end
end

Edit: The main class probably needs a destructor and a slightly more sophisticated implementation of GetPrivateProperties so that when an instance of the main class is destroyed its private properties are also removed from the map. Otherwise, memory usage can only go up. Left as an exercice to the reader...

Related Solutions

MATLAB: Is it possible to temporarily disable the private attribute of object properties in debug mode in MATLAB 7.9 (R2009b)

The ability to temporarily disable the private attribute of object properties does not currently exist in MATLAB 7.9 (R2009b). You can access the private properties of objects while debugging using either of the following methods:

1. Temporarily set the GetAccess attribute of the properties to public

2. Create a public method to display the contents of the private properties, as in the following class definition. This method can use Meta-Classes to analyze the class definition and determine all property names.

classdef test
    properties(SetAccess= private, GetAccess=private)
        a = 'a'; 
        b='b'; 
    end
    properties
        c='c'; 
        d='d';
    end
      methods
          function mydisp(obj)    
             % To display the private data
             m = metaclass(obj);
             metaProps = m.Properties;
             nProps = numel(metaProps);
             disp('Properties:')
             for n=1:nProps           
                 fprintf(' %s:  %d (SetAccess = %s; Get Access = %s)\n',...
                     metaProps{n}.Name,metaProps{n}.DefaultValue,...
                     metaProps{n}.SetAccess, metaProps{n}.GetAccess)
             end        
          end
      end
  end

MATLAB: Modifying an immutable/protected variable of a subclass in a superclass method

You're trying to break the fundamental model of OOP: encapsulation. The whole concept of protected properties is that only the class (or its subclasses) can modify them. A superclass has no way to modify the properties of its subclasses. For that matter, there's no guarantee that a subclass would have the propery that it's trying to modify.

Secondly, why are you trying this indirect method for setting properties? Can't you just set the properties of the subclass the normal way? Or even just override your setProperties method in the subclass?

If you really want to set the properties from the superclass, what you can do though is have a method setsubProperties in the superclass that you then override in the subclass. You dispatch to this method from the setProperties method:

classdef Sup < handle %has to be a handle class to modify its own properties
    methods
       function setProperties(this, varargin)
           this.setsubProperties(varargin);
       end
   end 
     methods (Access = protected)
         function setsubProperties(this, varargin)
              error('function must be overriden');
         end
     end
  end
classdef sub < Sup
    methods (Access = proteced)
       function setsubProperties(this, varargin)
           for varg = 1:2:numel(varargin)
               %...
           end
       end
    end
 end

Best Answer

Related Solutions

MATLAB: Is it possible to temporarily disable the private attribute of object properties in debug mode in MATLAB 7.9 (R2009b)

MATLAB: Modifying an immutable/protected variable of a subclass in a superclass method

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