MATLAB: Use of Persistent Variables in Class Methods Producing Incorrect Result.

classMATLABmethodsobject-orientedooppersistent

I am attempting to make use of a persistent variable within a class method. However, invoking the method from different instances is producing incorrect results. Here is a simple case of what I mean:
CLASS:
classdef MYCLASS < handle
      properties(GetAccess = 'private', SetAccess = 'private')      
          m_Count
      end   
      methods(Access = 'public')
          %constructor
          function obj = MYCLASS
              obj.m_Count = 0;
          end
          function out = DO_SOMETHING_MOUSE(obj)
              persistent n
              if isempty(n)
                  n = 0;
              end
              n   = n+1;
              out = n;
          end
          function out = DO_SOMETHING_CAT(obj)
              obj.m_Count = obj.m_Count + 1;
              out = obj.m_Count;
          end
      end  
   end
MATLAB FILE:
clear all
clear classes
clc
Instance_A = MYCLASS;
Instance_B = MYCLASS;
n = Instance_A.DO_SOMETHING_MOUSE
n = Instance_B.DO_SOMETHING_MOUSE
n = Instance_A.DO_SOMETHING_CAT
n = Instance_B.DO_SOMETHING_CAT
COMMAND WINDOW RESULTS:
a =
       1
b =
       2
a =
       1
b =
       1
>>
Here you can see that we call the DO_SOMETHING_MOUSE method from two different instances of the class, yet, the value of the persistent variable "n" was somehow shared between instances.
The result we should have gotten is that which was illustrated by the call to the DO_SOMETHING_CAT method. Each instance had it's own value correctly stored.
What's wrong?

Best Answer

This is the expected behavior. Persistent variables are the same as global variables expect for the fact that these variables can be accessed only within the function in which they are created. These variables retain their value till they are cleared from the memory.
When you created two different instances of the class, two independent instances were created with their own properties, whereas only one instance of the persistent variable was created in the memory. Therefore both objects access the same memory for the persistent variable
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