MATLAB: OOP: lazy dependent property

classdependent propertyoop

In a class, I have a dependent property that's expensive to calculate. It only depends on one other property, call it "value" in the class, so I'm trying to prevent it from re-calculating unless value changes.
The snippet below works, but it shows a warning about setting the property value for lazy in the set method for value. Is there a better way to do this?
classdef MyClass < handle
      properties
          value;
      end
      properties (Dependent)
          output;
      end
      properties (Access = private)
          lazy = false;
          cachedOutput;
      end
      methods
          function obj = MyClass(value)
              obj.value = value;
          end
          function set.value(obj, value)
              obj.lazy = false; % warning here
              obj.value = value;
          end
          function res = get.output(obj)
              if obj.lazy
                  res = obj.cachedOutput;
              else
                  res = expensive_function(obj.value);
                  obj.cachedOutput = res;
                  obj.lazy = true;
              end
          end
      end
end
function res = expensive_function(value)
    res = value + 1;
end

Best Answer

I've seen a recommendation to use persistent variables in expensive_function
    function res = expensive_function(value)
        persistent old_value old_res
        if not( isempty( old_value ) ) && value == old_value
            res = old_res;
        else 
            res = value + 1;
            old_res = res;
            old_value = value;
        end
    end
whether it is better I don't know.
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