MATLAB: How to avoid running superclass constructor

MATLAB

You have defined a class derived from a parent class with a constructor. There is a constructor in the derived class. MATLAB implicitly runs the constructor of parent class and I do not want in my case. How can I avoid MATLAB implict superclass constructor call? Help me out.

Best Answer

You cannot avoid the superclass constructor being called (explicitly or implicitly) from the subclass constructor. From the documentation: "If you do not make an explicit call to a superclass constructor from the subclass constructor, MATLAB makes the implicit call when accessing the object."

If you don't want your subclass constructor to call the superclass constructor, are you sure that you want the subclass to inherit from the superclass?

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MATLAB: Super class get callers name

Found it. Just call this:

 me = class(obj);

this gives the name of the created subclass. I call it in the constructor of the superclass:

 function obj = mySuperClass() %constructor
   me = class(obj);
   obj.name = me;
 end

MATLAB: Anyone know how to create a multidimensional subclass constructor

That's a very interesting question and I think it shows another problem with matlab class design.

The problem you'll encounter when constructing a derived object (let's call it B) is that in the superclass constructor, obj is still of class B and thus the line obj(n, 1) = A is going to cause an error, since A can't be converted to B. In A constructor obj should never be of type B.

There is an ugly workaround, use eval to construct the array of the required type. You'll end up with:

classdef A
   properties 
      a;
   end
   methods
      function this = A(arg1, arg2, arg3)
         if nargin == 0   %to support array construction
            return;
         else
            this(numel(arg1), 1) = eval(class(this)); %use eval to invoke the correct constructor
            arg1 = num2cell(arg1); [this.a] = arg1{:};  %distribute arg1 into each object
         end
      end
   end
end
classdef B < A
   properties
      b;
   end
   methods
      function this = B(Barg, arg1, arg2, arg3)
         if nargin == 0  %can't call base constructor inside if, so build base constructor arguments 
            args = {};
         else
           args = {arg1, arg2, arg3};
         end
         this@A(args{:}); %and call base constructor
         if nargin > 0
            Barg = num2cell(Barg);
            [this.b] = Barg{:};
         end
      end
   end
end

I'm going to raise that as an issue with mathworks as this shows that there is no decent way of initialising an object array. Assigning to the last element of array is fragile and breaks under your circumstances. I really hate that constructing an object and an array of object is done in the same constructor.

Best Answer

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MATLAB: Super class get callers name

MATLAB: Anyone know how to create a multidimensional subclass constructor

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