# How to efficiently use dependent properties if dependence is computational costly?

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Michael Baumgart el 8 de Mayo de 2014
Comentada: Jan Kappen el 5 de Mzo. de 2024
Hello!
I want to design a class where some properties are dependent on others. I understand the general concept of Matlab OOP for dependent properties: the property is recalculated each time it is accessed.
But if these calculations/dependencies are costly and the dependent properties are often accessed by methods within the class, what are you suggesting to do. Basically, it would suffice to recalculated the property each time its parents properties are updated.
If I do so, I get a warning that accessing another property from the set method of an independent property is not recommended. What else can I do?
Cheers Michael
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Jacob Halbrooks el 8 de Mayo de 2014
Editada: Jacob Halbrooks el 8 de Mayo de 2014
I would recommend you add a method to compute and update the value of your dependent property and then call that method from the setters for each property that updates it. This single-sources the computation of that property, caches it to avoid unnecessary re-computation, and satisfies MATLAB Code Analyzer.
Here is an example, where Area of a Rectangle depends on Width and Height and is updated when each of those is set:
classdef Rectangle < handle
properties
Width = 10;
Height = 20;
end
properties(SetAccess = private)
Area = 200;
end
methods
function set.Width(obj, v)
obj.Width = v;
obj.updateArea;
end
function set.Height(obj, v)
obj.Height = v;
obj.updateArea;
end
end
methods(Access = private)
function updateArea(obj)
obj.Area = obj.Width * obj.Height;
end
end
end
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Trym Gabrielsen el 26 de Oct. de 2023
Ok, thank you so much!
Jan Kappen el 5 de Mzo. de 2024
I'm using that pattern in handle classes too, but how to implement it in value classes? Updating dependent properties in the update Method does not work because the setter & getter do not return the object.
Thanks :)

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