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

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Christian Veenstra 2017-12-5

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评论： Greg 2017-12-5

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...

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Greg 2017-12-5

If my recommended answer doesn't work, you might be able to do evalin('caller','nargin') to determine if multiple set commands were issued.

This is a VERY bad idea, for various reasons. Use at your own risk.

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Answer 1

Greg 2017-12-5

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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