Matlab: Reference to a handle object - matlab

Question

Can I create a reference to a handle object in a way that I can replace the object itself at one point and the references will be updated?
Example:
classdef IShifter < handle
methods (Abstract)
x = Shift(this, x);
end
end
classdef Shifter1 < IShifter
methods
function x = Shift(this, x)
x = circshift(x, 1);
end
end
end
classdef Shifter2 < IShifter
methods
function x = Shift(this, x)
x = [ 0 ; x ];
end
end
end
classdef Item
properties (Access = 'private')
shifter; % should be a pointer/reference to the object which is in the respective parent container object
end
methods
function this = Item(shifter)
this.shifter = shifter;
end
function x = test(this, x)
x = this.shifter.Shift(x);
end
end
end
% note this is a value class, NOT a handle class!
classdef ItemContainer
properties
shifter;
items;
end
methods
function this = ItemContainer()
this.shifter = Shifter1;
this.items{1} = Item(this.shifter);
this.items{2} = Item(this.shifter);
end
function Test(this)
this.items{1}.Test( [ 1 2 3] )
this.items{2}.Test( [ 1 2 3] )
end
end
end
Then, the output should be:
items = ItemContainer();
items.Test();
[ 3 1 2 ]
[ 3 1 2 ]
items.shifter = Shifter2;
items.Test();
[ 0 1 2 ]
[ 0 1 2 ]
But instead it is:
items = ItemContainer();
items.Test();
[ 3 1 2 ]
[ 3 1 2 ]
items.shifter = Shifter2;
items.Test();
[ 3 1 2 ]
[ 3 1 2 ]
because assigning a new Shifter object to parent object items does not update the references in the containers.
I am looking for something like in C where all the "shifter" properties are pointers and I can put whatever Shifter object I want into this "address".
ItemContainer and Item are not handle classes.
I want to avoid using events to update the references or implementing a set method to update the references

Answer 1

The pass-by-reference concept in Matlab only goes so far (and is mostly limited to handle-classes anyway). It does not go as far as you'd like it to go.
If you don't want to use a set method, you can make items a dependent property with a get method that returns {this.shifter,this.shifter}
According to your comments, items is a bit more complicated than just a cell array. Thus, you may want to set up your object with a property itemsStore (or itemsCache, or whatever name you prefer for something that temporarily stores items), and a dependent property items. The get method to items checks whether itemsStore is empty; if yes, it reconstructs the item array and stores it in itemsStore, if not, it just returns the contents of itemStore. Additionally, you need to add a set method to shifter that empties itemsStore, so that items needs to be recreated. Note that MLint will give you a warning that a set method for a property shouldn't write into another property. This warning is meant to tell you that when you have saved an object and then load it again from disk, all the set methods will be executed. Depending on the order of execution, set methods that write into other properties may create unexpected results. In your case, it's no problem because an emptied itemStore is something that your code is designed to handle. If you want, you can right-click on the MLint warning, disabling it for that line.

Answer 2

Unfortunately I don't think this is possible in Matlab.
However, you can use a set method or subsasgn to redefine the content of items{1} and items{2} when item is defined. Then you will be able to get the behavior you're asking for.
Best,