On dependent properties: Is this poor Object Oriented Programming?

Hi, I have a class C1 with a dependent property d and another class C2 which inherits from C1.

When property d is called from C2, it naturally goes through C1. I would like the d coming from C2 to be a transformation of the d coming from C1.

What I did is to create an auxiliary function (not a new method) that is called by C1. The function does what C1 would do to get d and then checks whether the input is a C2 object in which case it transforms d.

Is this bad programming? Would you do it differently?

Thanks,

Answer 1

[Adam]

I would usually use the idea of a protected function that extends the base class.

So the base class function is of the type:

function d = get.d( obj )
   % base class implementation here
   d = doGetD( obj, d )
end

with an empty protected implementation of doGetD in the base class and an implementation that extends the base class in the derived class.

[Patrick Mboma]

Besides the fact that one has to modify the base class, this definitely works. GREAT THANKS !!!

I ended up doing the following

classdef C1
  properties(dependent)
  d
  end
  methods
    function d=get.d(this)
     d=first_pass(this);
     d=doGetD(this,d);
    end
    function d=doGetD(~,d)
    end
  end
end

classdef C2 < C1
  methods
    function d=doGetD(~,d)
     d=transform(d);
    end
  end
end

[Guillaume]

You really should move your doGetD into a protected block just as in my example.

Answer 2

[Guillaume]

No, it's not very good as your base class C1 now contains implementation that belongs to the derived class C2.

Rather than calling an auxiliary function in C1 d getter, you should call a private class method, that you then override in class C2.

[Patrick Mboma]

Guillaume, Thanks for the reply. I totally agree with the fact that C1 contains an implementation that belongs to a derived class and that is exactly why I did not like the solution.

I do not, however, understand exactly what you are saying in the rest of your reply. Could you, please, be more explicit? property d whether in C1 or in C2 has to be called with a function with the same name.

[Guillaume]

Actually the method you call needs to be protected

classdef C1
   properties (Dependent)
      d;
   end

   methods 
      function value = get.d(this)
         value = getdimplementation(this);
      end
   end

   methods (Access = protected)
     function value = getdimplementation(this)
        %actual implementation of dependent property for C1
     end
   end
end  %end of C1 definition

classdef C2 < C1
   methods (Access = protected)
      function value = getdimplementation(this)
        %actual implementation of dependent property for C2
      end
   end
 end

[Patrick Mboma]

Thanks Guillaume,

There is nowhere I can see that d is first processed in C1 and then transformed in C2. Any workaround or maybe I am missing something?

[per isakson]

"There is nowhere I can see" &nbsp Use the "debugger" to step through the code and you will see that it works automagically.