How to create a "one-way dependency" within Matlab handle class

Question

I am fairly new to Matlab, and I was wondering if there is a way to create a "one-way handle class".

To explain better, lets say I have a class called test_class, with properties "prop1" and "prop2"

test_1 = test_class(5,10)
test_2 = test_1

I wanted changes applied to properties within test_1 (parent) to affect test_2 (child), but I do not want changes in test_2 to affect test_1, so

test_1.prop1 = 20;
test_2.prop1: 20

test_2.prop2 = 30;
test_1.prop2: 5

Is there a way to create such a "one-way dependecy"?

Thanks in advance!

Answer 1

You can do this without getting into the difficulties of subasgn by leveraging property set listeners. This way you don't need ot get in the business of holding on to and managing all of the children copies. This looks something like the following:

classdef test_class < matlab.mixin.Copyable

    properties(SetObservable)
        prop1
        prop2
    end

    properties
        prop3
    end

    methods
        function obj = test_class(in1, in2, in3)
            obj.prop1 = in1;
            obj.prop2 = in2;
            obj.prop3 = in3;
        end
        function ref = make_dependent_reference(obj)
            ref = copy(obj);

            cls = metaclass(obj);
            observableProps = cls.PropertyList.findobj('SetObservable',true);
            for ct =1:numel(observableProps)
                obj.addlistener(observableProps(ct).Name, 'PostSet', ...
                    @(prop,evd)ref.update_dependent_reference(prop,evd));
            end
        end
    end
    methods(Access=private)
        function update_dependent_reference(ref, prop, evd)
            ref.(prop.Name) = evd.AffectedObject.(prop.Name);
        end
    end
end

Note, this requires the properties to be SetObservable, you can either choose to make the reference updates to those properties ignore properties that are not SetObservable like I've shown above with the findobj call or you can instead operate on all properties and let the addlistener call error out for any properties that are not SetObservable.

>> t = test_class(5,10,15)

t = 

  test_class with properties:

    prop1: 5
    prop2: 10
    prop3: 15

>> ref = t.make_dependent_reference

ref = 

  test_class with properties:

    prop1: 5
    prop2: 10
    prop3: 15

>> ref.prop1 = 6

ref = 

  test_class with properties:

    prop1: 6
    prop2: 10
    prop3: 15

>> t

t = 

  test_class with properties:

    prop1: 5
    prop2: 10
    prop3: 15

>> t.prop2 = 11

t = 

  test_class with properties:

    prop1: 5
    prop2: 11
    prop3: 15

>> ref

ref = 

  test_class with properties:

    prop1: 6
    prop2: 11
    prop3: 15