Why is calling a superclass constructor after a use of the object not allowed?

I have a subclass “subclass” of two classes “classA” and “classB”, which are in turn subclasses of “superclass”. Here is the class tree:

The superclass has two properties x and y. The classes “classA” and “classB” each do something special to initialize x and y, respectively. Then I want “subclass” to call both the “classA” and “classB” constructors to initialize x and y simultaneously. But the way the classes are built, I run into a snag.

Here are the definitions of the classes:

superclass.m:

classdef superclass
    
    %% PROPERTIES
    properties
        x;
        y;
    end
    
    %% METHODS
    methods
        function obj = superclass(x,y)
            % Initialize the properties
            obj.x = x;
            obj.y = y;
        end
    end
    
end

classA.m:

classdef classA < superclass
    
    %% PROPERTIES
    properties
        a;
    end
    
    %% METHODS
    methods
        % Constructor
        function obj = classA(a,y,z)
            x = a*z;
            obj@superclass(x,y);
            obj.a = a;
            obj.z = z;
        end
    end
    
end

classB.m:

classdef classB < superclass
    
    %% PROPERTIES
    properties
        b;
    end
    
    %% METHODS
    methods
        % Constructor
        function obj = classB(x,b,z)
            y = z+b;
            obj@superclass(x,y);
            obj.b = b;
            obj.z = z;
        end
    end
    
end

subclass.m:

classdef subclass < classA & classB
    
    %% METHODS
    methods
        % Constructor
        function obj = subclass(a,b,z)
            obj@classA(a,0,z);
            obj@classB(obj.x,b,z); % Why is this not allowed and how do I work around that
                                   % without redoing the calculations done in classes "classA" and "classB"?
        end
    end
    
end

This gives the following error message:

"A constructor call to superclass classB appears after the object is used, or after a return."

A couple of questions:

1) Why is calling a superclass constructor after a use of the object not allowed?

2) How do I work around that without redoing the calculations done in classA and classB? I feel like I might to redesign the class hierarchy. But it just bugs me that it can’t be done like above.

I use Matlab R2019a on Windows 10.

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I can only speculate as to why it would not be allowed, but I assume there are hazards in using an object that is not finished being constructed…like feeding a baby that is only half way through being born, or driving a car that’s only half assembled.

Below is how I would re-implement. In your original design, it doesn’t make sense to me that the classB constructor should have to set x if it has already been set in classA.

classdef superclass
    
    %% PROPERTIES
    properties 
        x;
        y;
    end
    
end

classdef classA < superclass
    
    %% PROPERTIES
    properties
        a
    end

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Why is calling a superclass constructor after a use of the object not allowed?

Why is calling a superclass constructor after a use of the object not allowed?