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

48 views (last 30 days)
Michael Baumgart on 8 May 2014
Commented: Vaughan Clarkson on 28 May 2024 at 2:10
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

Jacob Halbrooks on 8 May 2014
Edited: Jacob Halbrooks on 8 May 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
Jan Kappen on 5 Mar 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 :)
Vaughan Clarkson on 28 May 2024 at 2:10
It would be a nice addition to the Matlab language if there were a "Dependent = push" option or similar (vs. a default of "Dependent = pull") which could automatically execute the equivalent of the set and update methods that @Jacob Halbrooks defines above. It would save the programmer a lot of refactoring effort whenever it's discovered that the "push" paradigm is more efficient than "pull".