MATLAB: How to make a sum of two numbers update if one of the terms is updated in MATLAB 7.9 (R2009b)

bydependdependentMATLABobjectspassreference

I have calculated a sum of 2 numbers – a and b:
a=3;
b=3;
c=a+b;
I then modify a and would like c to update:
a=4;
c
However, c remains the same, as a, b, and c are of class double which is a value class. How can I write a custom handle class that would implement this functionality?

Best Answer

Define a custom class MYDOUBLE as follows:
classdef mydouble<handle
      properties(SetObservable)
          value
      end
      methods
          function obj=mydouble(v)
              obj.value=v;
          end
          function update(obj,src,event,c,b)
              c.value= obj.value+b.value;
          end
      end
end
You can then use the following code to update the value of the sum of two numbers:
clear classes
%create 3 mydouble. the 3rd one will be the sum of the first two
a = mydouble(5);
b = mydouble(4);
c = mydouble(a.value+b.value);
% add listeners to objects a and b so that they could listen for the change in their % property 'value' and update the sum c
addlistener(a,'value','PostSet',@(src, event) a.update(src, event,c, b));
addlistener(b,'value','PostSet',@(src, event) b.update(src, event,c, a));
% test the update
c.value
 ans = 
        9
a.value = 15;
c.value
 ans = 
       19
b.value = 30;
c.value
 ans =
        45
Please refer to the documentation for more information on Defining Events and Listeners:
web([docroot '/techdoc/matlab_oop/brb6gnc.html'])
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