How to set object property to Abstract class

I am getting errors when I try to set an object property type to an Abstract class "matlab.mixin.Heterogeneous" as below:

classdef demoClass
  properties
    TestProperty matlab.mixin.Heterogeneous   
  end
  methods
    function obj = demoClass
      % constructor that does not affect the property
    end
  end
end

The error I get is

>> demoClass
Error defining property 'TestProperty' of class 'demoClass'. Class matlab.mixin.Heterogeneous is abstract. Specify a default value for property TestProperty.

Answer 1

[MathWorks Support Team]

To specify an Abstract class as a property for a MATLAB class, you must also specify a default value for the property which is a class that is derived from the abstract class you specified.

The code below demonstrates how the code you provided might be modified to accomplish this workflow.

classdef demoClass
  properties
    TestProperty matlab.mixin.Heterogeneous = rootClass
  end
  methods
    function obj = demoClass
      % constructor that does not affect the property
    end
  end
end

classdef rootClass < matlab.mixin.Heterogeneous
  methods
    function obj = rootClass
    end     
  end
end

And now you should be able to instantiate an instance of "demoClass":

>> demoClass
ans = 
  demoClass with properties
    TestProperty: [1×1 rootClass]

Answer 2

[Jim Svensson]

It is stupid Matlab language design. It should be normal to define a property to be an abstract class type. As long as it is empty (array with 0 elements) it is not a problem, and then only assign concrete sub-classes to the property.