Property validation in subclass

Hello everyone, i am new to the OOP in Matlab.

I have a superclass SimpleList with the property set, which is an array with any kind of data in it.

 classdef SimpleList < handle
    % SimpleList

    properties
        set(:,1)
    end

    methods
     .
     .
     .
    end

 end

And a subclass ObjList, where the array should only contain objects of a specific class

 classdef ObjList < SimpleList
    % ObjectList

    properties
    end

    methods
     .
     .
     .
    end

 end

My Question is: How do i validate the property in ObjList?

Thanks in advance!

Answer 1

[Guillaume]

Note: I would recommeng giving a name other than set to your property. That name is already overloaded enough by matlab.

You can create a property validation function in the class that define the property using the syntax (for handle classes):

function set.propertyname(object, valuetoset)
    %validation code
end

with your property name this would be

function set.set(this, value)     %See why you should rename the property?
   if ~strcmp(class(value), somevalidclass)
        error('invalid class supplied to set');
   end
   this.set = value;
end

However, as I said, this property set method must be implemented in the class that defines the property, that is your base class, not the derived class. The workaround is from the set method to call another method that does the validation and is overridden by the derived class:

classdef SimpleList < handle
    properties
        set;
    end

      methods
          function set.set(this, value)
              isok = this.validateset(value);  
              if ~isok
                 error('invalid type of variable for set property)
              end
              this.set = value;  %DO NOT set the value is a subfunction or you'll get infinite recursion
          end
      end

      methods (Access = protected)
          function isok = validateset(this, value)
             isok = true;
          end
      end
  end
classdef ObjList < SimpleList
    methods (Access = protected)
        function isok = validateset(this, value)
           isok = strcmp(class(value), 'double');
        end
    end
end

Answer 2

[Adam]

In general I do this kind of thing via delegation from the superclass set function. Your property declaration confuses me though. Don't call a property 'set', it is asking for trouble. Also using (:,1) in the property block doesn't make much sense to me - is it even valid syntax there?

So to give an example:

classdef mySuperClass < handle

     properties
        myProp;
     end

     methods
        function set.myProp( obj, myPropVal )
           myPropVal = doValidateMyProp( obj, myPropVal );

           obj.myProp = myPropVal;
        end
     end

     methods( Access = protected )
        function myPropVal = doValidateMyProp( obj, myPropVal )
        end
     end

end

classdef mySubClass < mySuperClass

     methods( Access = protected )
        function myPropVal = doValidateMyProp( obj, myPropVal )
           % Do some validation
        end
     end

end

You don't have to return the value out of the function - it depends what type of validation you are doing. If you just want it to throw an error then get rid of the output type, but if, for example, you use validatestring the output argument can be useful.

I left the body of the doValidateMyProp function empty in the superclass - it is up to you what you put in here. Because I didn't make it abstract this will get called if your subclass does not override the function so it isn't compulsory for the subclass to do this.

[Guillaume]

Great minds think alike, or somesuch...

(:, 1) is indeed not valid. I assumed it was a typo.

I forgot to mention in my answer that if the base class is not meant to be used as a container on its own, then ideally it should be abstract.