unexpected behavior with matlab.mix​in.Heterog​eneous

There seems to be an issue with inheritance when using

    "matlab.mixin.Heterogeneous."

To illustrate consider two objects (code at bottom): Child, which inherits from Parent. The superclass method "changeParentVariable" is useless only when everything inherits from matlab.mixin.Heterogeneous. One would hope that root of inheritance (handle or matlab.mixin.Heterogeneous) would be immaterial. How can I make correct the behavior of matlab.mixin.Heterogeneous?

Behavior when everything inherits from "handle:"

    >> test = Child(1,2)

    test = 

      Child with properties:

         childVariable: 2
        parentVariable: 1

    >> changeParentVariable(test,3)

    >> test

    test = 

      Child with properties:

         childVariable: 2
        parentVariable: 3

Behavior when everything inherits from "matlab.mixin.Heterogeneous:"

    test = Child(1,2)

    test = 

      Child with properties:

         childVariable: 2
        parentVariable: 1

    >> changeParentVariable(test,3)
    >> test

    test = 

      Child with properties:

         childVariable: 2
        parentVariable: 1

...the superclass method was unable to modify the object when everything inherits from "matlab.mixin.Heterogeneous."

THE CODE

    classdef Parent < handle     % or matlab.mixin.Heterogeneous
        properties
            parentVariable = [];
        end
        methods
            function obj = Parent()
               obj.parentVariable = 0;
            end

            function changeParentVariable(obj,a)
               obj.parentVariable = a;
            end 
        end
    end

    classdef Child < Parent
        properties
            childVariable = [];
        end
        methods(Sealed)
            function obj = Child(a,b)
               obj = obj@Parent();

               obj.parentVariable = a;
               obj.childVariable = b;
            end
        end
    end

Answer 1

[Geoff Hayes]

Scott - I think that you are encountering the different behaviours of using a handle class versus a value class. From comparing handle and value classes,

A value class constructor returns an instance that is associated with the variable to which it is assigned. If you reassign this variable, MATLAB® creates a copy of the original object. If you pass this variable to a function, the function must return the modified object.

A handle class constructor returns a handle object that is a reference to the object created. You can assign the handle object to multiple variables or pass it to functions without causing MATLAB to make a copy of the original object. A function that modifies a handle object passed as an input argument does not need to return the object.

Since matlab.mixin.Heterogeneous is a value class (see handle compatibility section of matlab.mixin.heterogeneous class) then you would have to modify your changeParentVariable to

 function [obj] = changeParentVariable(obj,a)
     obj.parentVariable = a;
 end

and change your call to

test = test.changeParentVariable(3); % or test = changeParentVariable(test,3)

so that the parent variable is updated as

 test = 
    child with properties:
       childVariable: 2
      parentVariable: 3

[Scott Rowe]

Thanks Geoff,

Yup, that makes sense, although considering objects as pass by value is...different.