Why won't my superclass method change my subclass object?

I am trying superclass / subclass relationships for the first time. I have defined a subclass, M, with two super classes, S & R. My subclass has data in it and I want to call a superclass method from each superclass to add data to the subclass.

When I call the superclass method, it is called and executes correctly on the subclass object. However, when it returns from the call, the subclass object remains unchanged. I'm sure it's something obvious I'm missing but I've searched the forums and can't quite seem to find what I'm looking for.

I created the following files as a generic example that illustrates what I'm seeing:

M.m:

classdef M < S & R

%M Summary of this class goes here

% Detailed explanation goes here

properties

data

end

methods

function obj = M(a, b, c)

%M Construct an instance of this class

% Detailed explanation goes here

obj@S(a,b);

obj@R(a,c);

obj.data = repmat([b c], a, 1);

disp('Original M Object:');

disp(obj);

disp(obj.data);

obj.addSdata;

disp('M Object after calling S Method:');

disp(obj);

disp(obj.data);

disp('M object after calling R Method:');

obj.addRdata;

disp(obj);

disp(obj.data);

end

end

end

S.m:

classdef S

%S Summary of this class goes here

% Detailed explanation goes here

properties (Constant)

Sdivisor = 3;

end

properties (Abstract)

data

end

properties (Access = private)

a

b

end

methods

function obj = S(Sa, Sb)

%S Construct an instance of this class

% Detailed explanation goes here

obj.a = Sa;

obj.b = Sb;

end

function obj = addSdata(obj)

%METHOD1 Summary of this method goes here

% Detailed explanation goes here

newb = obj.b / obj.Sdivisor;

newcol = repmat(newb, obj.a, 1);

obj.data = [obj.data newcol];

disp('Object in S Workspace:');

disp(obj);

disp(obj.data);

end

end

end

R.m:

classdef R

%R Summary of this class goes here

% Detailed explanation goes here

properties (Constant)

Rmultiplier = 3;

end

properties (Abstract)

data

end

properties (Access = private)

a

c

end

methods

function obj = R(Ra, Rc)

%R Construct an instance of this class

% Detailed explanation goes here

obj.a = Ra;

obj.c = Rc;

end

function obj = addRdata(obj)

%METHOD1 Summary of this method goes here

% Detailed explanation goes here

newc = obj.Rmultiplier * obj.c;

newcol = repmat(newc, obj.a, 1);

obj.data = [obj.data newcol];

disp('Object in R Workspace:');

disp(obj);

disp(obj.data);

end

end

end

testM.m:

Mo = M(10,102,100);

Output:

>> TestM

Original M Object:

M with properties:

data: [10×2 double]

Sdivisor: 3

Rmultiplier: 3

102 100

102 100

102 100

102 100

102 100

102 100

102 100

102 100

102 100

102 100

Object in S Workspace:

M with properties:

data: [10×3 double]

Sdivisor: 3

Rmultiplier: 3

102 100 34

102 100 34

102 100 34

102 100 34

102 100 34

102 100 34

102 100 34

102 100 34

102 100 34

102 100 34

M Object after calling S Method:

M with properties:

data: [10×2 double]

Sdivisor: 3

Rmultiplier: 3

102 100

102 100

102 100

102 100

102 100

102 100

102 100

102 100

102 100

102 100

M object after calling R Method:

Object in R Workspace:

M with properties:

data: [10×3 double]

Sdivisor: 3

Rmultiplier: 3

102 100 300

102 100 300

102 100 300

102 100 300

102 100 300

102 100 300

102 100 300

102 100 300

102 100 300

102 100 300

M with properties:

data: [10×2 double]

Sdivisor: 3

Rmultiplier: 3

102 100

102 100

102 100

102 100

102 100

102 100

102 100

102 100

102 100

102 100

As you can see, it creates the object correctly and sets up the initial data. Further, when I call the superclass methods, it uses the subclass object, M, and changes it as expected while it is running. So up to that point, it runs as I'm expecting.

Once it exits the method, however, the subclass object returns to its original state. This happens for both superclass methods.

What do I need to change to get this to work the way I want?

[Captain Karnage]

I also tried declaring the methods "addRdata" and "addSdata" in M.m as follows:

function obj = addRdata(obj)

addRdata@R(obj);

end

function obj = addSdata(obj)

addSdata@S(obj);

end

and got the exact same result.

Answer 1

[Matt J]

You need,

obj=obj.addSdata;
obj=obj.addRdata;

Or, read about handle classes.

[Captain Karnage]

Well, I knew it was going to be something simple like that.

And... now I realize I need that everywhere in my real program, not just the functions represented by these two. I guess I assumed that anything passing the class object to an internal method that changes the object would change the object without obj =. I just didn't notice the issue until it become more glaringly obvious.

Thank you for your help.

[Matt J]

I guess I assumed that anything passing the class object to an internal method that changes the object would change the object without obj =

Well, that is indeed the case for a handle class (see my earlier link), so you might consider inheriting from handle as well, if you truly need that behavior.

[Captain Karnage]

I'll definitely be looking into handle objects, thank you. For now, I have it working with that simple change.

Also... as a note in case anyone else ever has a similar issue. This solution worked immediately on the example code I provided. When I put it into my real program, it didn't seem to work at first, I was getting the same result. Then I realized I left in the subclass methods using the @ reference to the superclass and those didn't have the obj = on them, either. So if anyone copied from that comment, just remove those subclass methods.