MATLAB: Dependent property is shown in the variable editor even before its get method

dependentMATLABoop

I have a class with a dependent property. But even before I invoke its get method, its value is shown in the Variable Editor. How can this happen, isn't a dependent property calculated on demand (i.e. calling its get method)? For an actual code, see e.g. the documentation .

Best Answer

"before I invoke its get method, its value is shown" Yes, that's is obviously the case, but I fail to find this behaviour described in the documentation. However, I think it's useful.
IIRC: The dependent property is calculated "in the background" when displayed in a tooltip or the Variable Editor. Several releases back, the dependent property was calculated by an explicit call to the get-function when required for a tooltip. That caused a lot of pain when there was a bug in the get-function.
Try the following steps
>> cdp = class_dep_prop();
  • set a breakpoint in the foo-method
>> cdp.foo
  • point at this to see a tooltip. Note that a value is displayed for x, but not for y.
  • replace b=(1:3); by b=(1:2); and repeat the steps. Now, a value is displayed for y.
This behaviour is better than the old one, which throw an error in the get-function. (Maybe, it would be even better to show something like y=-error- in the tooltip when there is a bug in the get-function.)
where
classdef class_dep_prop < handle
      properties
          x = 1;
      end
      properties ( Dependent = true )
          y
      end
        methods
            function  val = get.y( this )
                a = (1:2);
                b = (1:3);
                c = a .* b;
                val = c * this.x;
            end
            function  val = foo( this ) %#ok<MANU>
                val = 17;
            end
        end
  end
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