MATLAB: How to disable modification to an object that is a property of another object in MATLAB 7.11 (R2010b)

MATLAB

I have a class A that contains a property which is is an object of handle class B. I want to implement a locking mechanism, which allows the user to instantiate class B, set it as a property of an object of class A, and then "lock" the property of object A.

Once the property is locked, changing the handle to object B should not be permitted. However with the locked handle, I should be able to access the object of class B, but not modify it.

Best Answer

Property access attributes cannot be modified at runtime in MATLAB.

However, there are ways to prevent the program from modifying the values of a property, once it has been "locked".

Approach 1:

Define the 'SetAccess' attribute for the property of class A that holds the object of class B as 'immutable'. Similarly define all properties of class B as 'immutable'. In this way, you can only set the values of the properties for the first time in the constructor.

Approach 2:

A more flexible approach is to define a flag property, and write your own code for 'set.propertyname' method in the class A. In this method, the property which contains the handle to object of class B, should be modified only if the flag is reset. Note that once the handle is available the user would still be able to read it, and modify the object of class B, but cannot modify the handle itself. As an example:

methods
       set.propertyname(object,value)
            % Write code for checking flag and assign value only if flag reset
       end
end

Further, to avoid modifying the object of class B, the value of flag would have to be queried from object of class A and implement a logic similar to the one above to make each property modifiable/not modifiable.

Related Solutions

MATLAB: How to set object property to Abstract class

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]

MATLAB: Changing variable (properties in class) by method

Your class is a value class as opposed to a handle class. See this documentation page for a description of the differences between the two. The "Modifying Value Objects in Functions" and "Modifying Handle Objects in Functions" sections on that documentation page describe what happens when you modify properties of an instance of each kind of class in a function or method. So you can either:

Define the methods in your value class to return the modified object, and call the methods with the object as both input and output.
Change your class to a handle class.

Best Answer

Related Solutions

MATLAB: How to set object property to Abstract class

MATLAB: Changing variable (properties in class) by method

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