MATLAB: Is it possible to tell if another set method call is coming up

set method

I have an object that does a somewhat long calculation, stores the result, and then lets the user use it. If they change certain properties then it needs to be recalculated. So, in the set method for those properties, I just call the precalculation method. Ideally, if the user changed multiple properties at the same time – for example, set(obj,'A',a,'B',b) – then it wouldn't do the calculation twice. Is it possible for me to check how the set method was called? Ideally I could write something like:

 classdef foo < matlab.mixin.SetGet
 properties (SetAccess=private)
    Expensive=[];
 end
 properties
    a=1;
    b=2;
 end
 methods
      function DoSomethingHard(obj)
         Expensive=SomeLongCalculation(obj.a,obj.b);
      end
      function set.a(obj,value)
         obj.a=value;
         if NoMoreSetCallsComingUp
            obj.DoSomethingHard;
         end
      end
      function set.b(obj,value)
         obj.b=value;
         if NoMoreSetCallsComingUp
            obj.DoSomethingHard;
         end
      end
 end
 end

Except I don't know what "NoMoreSetCallsComingUp" would look like. Is this possible? Currently I'm just doing a lot of unnecessary computations…

Best Answer

I can't test it on this machine to confirm, but you should be able to define set for your class (as opposed to set.a and set.b individually). Then, parse the parameter-value pairs and call doSomethingHard at the end.

methods
    function DoSomethingHard(obj)
       Expensive=SomeLongCalculation(obj.a,obj.b);
    end
    function set(obj,varargin)
       % Obviously want better input checking...
       for iarg = 1:2:length(varargin)
         obj.(varargin{iarg}) = varargin{iarg+1};
       end
       % Best practice is to call methods method(obj) vs. obj.method
       % avoids confusion between methods and properties 
       DoSomethingHard(obj);
    end
end

Related Solutions

MATLAB: [Warning] Why is it bad practice to set additional class properties when using a set method (prompting a warning)

Be very careful not to get yourself into a recursive situation like the class I posted earlier this month for this Answer does.

I would probably make B a Dependent property with a get.B method that accesses the A property. See this documentation page for some information about dependent properties.

A couple observations about your class:

Your default value for the A property does not satisfy the size validation you've listed in your file. Either the default value should be [5; 1] or you should require A to be of size [1 2].
Your doThing method doesn't make sense to me. As written it would make B out of sync with A. You could have doThing update A then the value of the Dependent property B would also be doubled. [I would not define a set.B method, or if I did I would implement it so it throws a user-friendly error message.]

        function obj = doThing(obj)
            obj.A = 2*obj.A;
        end

MATLAB: Is calling a superclass constructor after a use of the object not allowed

I can only speculate as to why it would not be allowed, but I assume there are hazards in using an object that is not finished being constructed...like feeding a baby that is only half way through being born, or driving a car that’s only half assembled.

Below is how I would re-implement. In your original design, it doesn't make sense to me that the classB constructor should have to set x if it has already been set in classA.

classdef superclass
    
    %% PROPERTIES
    properties 
        x;
        y;
    end
    
end

classdef classA < superclass
    
    %% PROPERTIES
    properties
        a
    end
    
    properties (Access=private)
        z
    end
    
    %% METHODS
    methods
        % Constructor


        function obj = classA(a,z,y)
            obj.x = a*z;
            obj.a = a;
            obj.z = z;
            if nargin>2
             obj.y=y;   
            end
        end
    end
    
end

classdef classB < superclass
    
    %% PROPERTIES
    properties
        b
    end
    properties (Access=private)
        z
    end
    
    %% METHODS
    methods
        % Constructor
        function obj = classB(b,z,x)
            obj.y = z+b;
            obj.b = b;
            obj.z = z;
            if nargin>2
               obj.x=x; 
            end
        end
    end
    
end

classdef subclass < classA & classB
    
    %% METHODS
    methods
        % Constructor
        function obj = subclass(a,b,z)
            obj@classA(a,z);  %set x but not y
            obj@classB(b,z);  %set y but not x  
        end
    end
    
end

Related Question