Setting a Base Class property from Derived class

Hello all..I am a begineer to OOPS in MATLAB . I need to set the property in baseclass from the derived class. How should I do that.. This is my example

DERIVED CLASS

classdef classA < classB 
  properties
     A=2; 
     b=3; 
  end

    properties
       mystring='MATLAB'; 
    end 
  end

BASE CLASS

classdef classB < classC    
   properties 
      myValue=[]     
   end

     methods
          %%REST OF THE CODE %%%        
     end
  end

I would like to set the the property myValue (which is in Baseclass) from the derived class. Can anyone help me out in this... Apologies if it's a newbie questions..

NOTE : I dont want to define that property in the derived class and get its value in base class. The reason is : I have lot of derived classes where I might need to set the property myVal (or) in some cases dont need to set it. So i need to be empty for my code in BASE CLASS

[per isakson]

What's the problem? What have you tried?

[Adam]

Please post the code you tried to do this (and especially the error messages) as standard usage of the get and set methods should work fine.

If you are trying to set a base-class property from the properties block of a derived class then this won't work - you have to do it from the code itself - e.g. in the constructor.

Ideally you should get used to using the property access specifiers on a properties block e.g.

properties( SetAccess = protected, GetAccess = public )
...
end

because it helps you create code less liable to bugs with better encapsulation - i.e. outside objects or functions cannot set these properties so you know only the class and its derived classes can do so.

However, the default access is public so that doesn't appear to be the source of your error because anything can set and get these properties.

[per isakson]

Moved to here by per isakson

Answer by Aryan Sinha about 1 hour ago

I was trying to use set and get methods ..But its erroring out

[Aryan Sinha]

classdef classA < classB 
  properties
     A=2; 
     b=3; 
  end
    properties
       mystring='MATLAB'; 
    end

    methods
      function setobj(obj)
      obj.myValue=1234;
      end
    end
end

[Aryan Sinha]

I was using something like this in my code... and It never sets the property/// may be I am going wrong somewhere

[per isakson]

• What do you exactly mean by: "I need to set the property in baseclass from the derived class." ? I would say set a property value of an object.
• You don't show classC. Is it a handle class?

[Aryan Sinha]

Class C is another Super class which is a handle class....

yes , I do mean that to override the SuperClass Property in BaseClass using get method

[Aryan Sinha]

This is just an example of what I am trying to do.. My code has lot of stuff in it with UnitTesting in it...

My question in a straight way was to overriding the super class properties in subclass using get method,,,

[Adam]

Ok, what you say there does hint at a problem, but does not seem to relate to the code example you showed using a home-made function called setObj. I will add an answer below relevant to your point in bold which may or may not be of use, depending exactly what your problem is.

Answer 1

[per isakson]

I tried this, which works fine. What do you try to do?

>> ca = ClassA
ca = 
  ClassA with properties:

             A: 2
             b: 3
      mystring: 'MATLAB'
       myValue: []
  >> ca.setobj
  >> ca
  ca = 
    ClassA with properties:

             A: 2
             b: 3
      mystring: 'MATLAB'
       myValue: 1234
  >>

where

classdef    ClassA < ClassB
    properties
        A=2;
        b=3;
    end
    properties
        mystring='MATLAB';
    end
    methods
        function setobj(obj)
            obj.myValue=1234;
        end
    end
end

and

classdef    ClassB < handle
    properties
        myValue=[]
    end
    methods
        %%REST OF THE CODE %%%
    end
end

One more trial. No problems, works according to documentation

>> ca = ClassA
ca = 
  ClassA with properties:

             A: 2
             b: 3
      mystring: 'MATLAB'
       myValue: []
  >> ca.myValue = 4321
  ca = 
    ClassA with properties:

             A: 2
             b: 3
      mystring: 'MATLAB'
       myValue: 4321

[Steven Lord]

This works because ClassB is a handle class. If it were not, your ClassA setobj method would need to return the modified object and you'd need to call it with an output argument.

Answer 2

[Adam]

Taking a bit of a guess from your comments above, this may be relevant to your problem, but either way it is hopefully useful information anyway.

When you have a property in a base class you are free to get and set this in the derived class (provided it has at least protected access. You would do this as you would anywhere simply by e.g.

myClass.myValue = 1234;

This will call get.myValue in the base class because it is a base class property. Everything here is fine.

What you cannot do is try to overide the get.myValue function in your derived class. myValue is a property of the base class and only the base class can define its get function. So you cannot overide this with different behaviour in different derived classes.

What you can do and I have done often in my work is a construct like the following:

classdef myBaseClass < handle
    
    properties( Dependent, Access = public )
      myValue = [];
    end
    
    methods
      function set.myValue( obj, value )
        doSetMyValue( obj, value );
      end
      
      function value = get.myValue( obj )
        value = doGetMyValue( obj );
      end
    end
    
    methods( Access = protected )
      doSetMyValue( obj, value )
      value = doGetMyValue( obj )
    end
    
  end

    classdef myDerivedClass < myBaseClass
      
      properties( Access = private )
        myValue_ = [];
      end
      
      methods( Access = protected )
        function doSetMyValue( obj, value )
          obj.myValue_ = value + 7;
        end
        
        function value = doGetMyValue( obj )
          value = obj.myValue_ + 7;
        end
      end
      
    end

    classdef myDerivedClass2 < myBaseClass
      
      properties( Access = private )
        myValue_ = [];
      end
      
      methods( Access = protected )
        function doSetMyValue( obj, value )
          obj.myValue_ = value * 2;
        end
        
        function value = doGetMyValue( obj )
          value = obj.myValue_ * 2;
        end
      end
      
    end

This is a completely contrived example that does something ridiculous, but shows the derived classes each defining the behaviour of getting and setting the base class property whilst still having the property defined in the base class and therefore available to all classes.

In this case the base class forces the derived classes to define this behaviour. You could also setup default behaviour in the base class so that derived classes only override it if they want to. Be careful doing this though, you need to store a second noon-dependent property. My first attempt, a little rusty from when I last did this setup, led me into infinite recursion! Using the above you would get, for example:

>> d = myDerivedClass;
>> d.myValue = 6

d = 

    myDerivedClass with properties:

      myValue: 20

>> d2 = myDerivedClass2;
>> d2.myValue = 6

d2 = 

    myDerivedClass2 with properties:

      myValue: 24