Matlab redfining properties for all instances of a class

I have a class I am working on that evaluates functions then uses some criteria to optimize those functions. I created a class for all of this. Everything seems to be working fine except the function that is supposed to drill down to the best answer. Below is an example of what it is doing:

 A.get_cases
ans =
           1          11         111         121        1211        1221        1321        1331
>> B=drilldown(A, 1)
B = 
  TRON handle with no properties.
  Methods, Events, Superclasses
>> 
>> A.get_cases
ans =
        1331

So it is redifining the properties of A even though the function only operates on B. What it does to B is just fine, but I do not understand why it is changing properties of A as well. Anyone know why this is happening and how to stop it?

I have included the function below. Any help would be greatly appreciated.

function new_instance=drilldown(old_instance, whichcase)
new_instance=old_instance;  %I was hoping the changes would only be to new_instance, but they
                            % appear to be happening to old_instance as well.
thesemaxes=new_instance.get_maxes{whichcase};
thesemins=new_instance.get_mins{whichcase};
newranges=cell(1,length(thesemaxes));
for i=1:length(thesemaxes)
    thisdiff=thesemaxes(i)-thesemins(i);
    thisinterval=thisdiff/10;
    thisrange=thesemins(i):thisinterval:thesemaxes(i);
    newranges{i}=thisrange;
end
indnames=new_instance.get_indnames;
new_instance.set_indvars(indnames, newranges); %This is the only step in the function that
                                               %changes properties of an object from my class.

end

Answer 1

[Matt J]

Remove the '<handle' inheritance from the classdef of A.

Or, if you still want A to be a handle object, then instead of doing

new_instance=old_instance;

you must write a method that uses the class constructor to create an unshared clone of A, and then do something like

new_instance=old_instance.clone();