Writing class in matlab with structures and not allowing user to modify them.

I am writing a new class for my project which contains many variables. So I have devided it into many class, lets say-- class "m" has properties m1, m2, m3; class "k" has properties k1,k2,k3, ... and so on). These classes are then imported to a class (say p), as shown below

classdef m
    properties 
        m1,m2,m3
    end
end
%%%
classdef k
    properties
        k1,k2,k3
    end
end
%%%
classdef p < m & k
...    
end

In this way all the elements are available as p.m1,p.m2,..., p.k1,p.k2,p.k3, ...., etc. Now my problem is that the class "p" has too many variables and looks messy.

Therefore I would like to keep the class in a structured way as-- p.m.m1, p.m.m2, p.m.m3...., p.k.k1, p.k.k2,... etc., For which I have following code.

classdef mod
    properties 
        m= struct('m1',1,'m2',2,'m3',3)
    end
end
%%%
classdef kal
    properties
        k= struct('k1',1,'k2',2,'k3',3)
    end
end
%%%
classdef p < mod & kal
...    
end

It achieves the above goal, but at the cost of allowing user to add elements to substructure, i.e.

p.s=5    % adding property is not allowed
p.m.s=5  % adding property is ALLOWED..! 

Is there any way to stop the user from adding/removing the properties to substructures.

Thanks..!

[Matt J]

These classes are then imported to a base class (say p), as shown below

Your terminolgoy is a bit confusing. Conventionally, in OOP, mod and kal would be called the base classes, while p is the child class or subclass.

[AM]

My bad. Thanks for pointing that out.

[Matt J]

lets say-- class "m" has properties m1, m2, m3; class "k" has properties k1,k2,k3, .

Where possible, you should be using a single vector variable, m , not individual scalar variables m1, m2, m3...

Answer 1

[Matt J]

You can define a set.property method like in the following. This will be inherited by any subclasses.

classdef myclass
 
    properties 
        m= struct('m1',1,'m2',2,'m3',3)
    end

    methods
        function obj=set.m(obj,val)

             if ~isstruct(val)||...
                ~isempty(setxor(fieldnames(obj.m), fieldnames(val)))
               error 'Not allowed'
             end
             obj.m=val;

        end

    end

end

>> obj=myclass; obj.m

ans =

struct with fields:

m1: 1

m2: 2

m3: 3

>> obj.m.m1=10; obj.m

ans =

struct with fields:

m1: 10

m2: 2

m3: 3

>> obj.m=5

Error using myclass/set.m (line 12)

Not allowed

>> obj.m.m4=5

Error using myclass/set.m (line 12)

Not allowed

Answer 2

[Matt J]

Couldn't you make the properties private/protected in mod and kal?

[AM]

You rightly pointed that out. I can do that, however, I don't want to stop user from seeing the changes in the variable. Since it is easier for a user to interact with workspace, it will be nice to have all changes reflected in the workspace. Additionally it would require much effort in writing set/get function, since there are many independent variables.

[Matt J]

however, I don't want to stop user from seeing the changes in the variable.

Make SetAccess=private/protected only. If GetAccess is still public, they will still be able to view and access the property values. Alternatively, you can overload disp() so that fully private properties are displayable at the command line:

https://www.mathworks.com/help/matlab/matlab_oop/displaying-objects-in-the-command-window.html

Additionally it would require much effort in writing set/get function, since there are many independent variables.

You shouldn't need set/get functions. Inside the classdef, you can access protected properties freely.

[AM]

Thanks for the suggestion. I understand it can be done for the first case. However, my question was slightly different. I would like to-- (i) keep the data in structured way as shown in the second case, (ii) prevent user from adding a new property or removing an existing property, and (iii) allow user to see/alter to the property's values. Please let me know if it is possible.

[Matt J]

I don't know what the two cases are that we are talking about. Please explain why SetAcccess and GetAccess method attribute settings will not do what you want.

[AM]

The two cases were explained in first question in this thread. Presume me as a beginner with the MALAB Class, so whenvever possible please elaborate with code. I belive SetAccess and GetAccess will result in first case (first question in thread). However, I would like to have a class with properties as shown below:

p.m.m1, p.m.m2, p.m.m3....,

p.k.k1, p.k.k2, p.k.k3,... , etc.

Now I looking for two things in this class.

• User should be able to access and modify the properties directly as

p.m.m3= 45      % user should be allowed to modify the variable
p.k.k1=-83      % user should be allowed to modify the variable

% user should be able to access the variables data/values
>> p.m.m3       
45
>> p.k.k1       
-83

• The user should NOT be able to change the class structure, that includes adding/removing a new variable. To clarify, consider a new property named 'extra'.

p.extra =30    % should not be allowed  (by default not allowed in a class)
p.m.extra =30  % should not be allowed  (this is yet to achieve)

I tried with the codes given in first question. Please let me know if it is possible.