Why do array of dynamical properties not behave like array of properties ?

Question

Thibaut Jacqmin 2017-1-25

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https://ww2.mathworks.cn/matlabcentral/answers/321878-why-do-array-of-dynamical-properties-not-behave-like-array-of-properties

评论： Thibaut Jacqmin 2017-1-27

Why do dynamical properties behave differently than usual properties when getting them ?

Let us say I have one array of object my_class1 in an object of class my_class2. Then I add dynamically a property to all the elements of this arry.

classdef my_class1 < dynamicprops
  property
     Pressure
  end
end
classdef my_class2 < handle
    properties
       my_prop = my_class1
    end
end
my_object = my_class1;
for i = 1:10
   my_object.my_prop(i) = my_class2;
   my_object.my_prop(i).addprop('Temperature');   
end

Then if I try to retrieve all the properties in one vector, what I would do with a non dynamical property would be

vec = [my_object.my_prop.Pressure];

However with a dynamical property it does not work I need to make a for loop :

for i = 1:10
  vec(i) = my_object.my_prop(i).Temperature;
end

Thanks a lot.

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Adam 2017-1-27

编辑：Adam 2017-1-27

That is certainly something else that would put me off using these. I have pondered on classes inheriting from dynamicprops numerous times, trying to think of a scenario when I would find it useful, but I never have done despite writing probably > 2000 classes in Matlab so far.

Every time I think of it I come to the same conclusion - if the property makes sense on the class then why isn't it a permanent property? I have many classes where I have such properties which, for some objects, I just leave empty and run an isempty test on when using. This tends to be my solution to this.

It's not necessarily better, it's just a preference because one of the (many many) reasons I like classes better than structs, even for simple stuff with no real methods, is that I can see the properties of the objects of that class just by looking at the class file - there are no hidden surprises like the christmas tree style of a struct to just hang things off anyhow. Dynamic properties feel to me a bit more like a cross between a class and a struct in a direction I'm not keen on. I've often thought of trying them out, see if I change my mind, but something like this would dissuade me further I think.

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