Can I detect array index inside setter method?

Is there a way to detect the index/position of the setted value inside a new defined setter method?

I mean, if I call

obj.Prop(idx) = val;

that

function set.Prop(obj,val)
    if % idx > 5
            
        val = ...;
        
    end
    obj.Prop = val;
end

does different calculations on specific indices.

THX

In MATLAB documentation is a short description I don't really understand________________________________________

Access Methods and Properties Containing Arrays

You can use array indexing with properties that contain arrays without interfering with property set and get methods.

For indexed reference:

val = obj.PropName(n);

MATLAB calls the get method to get the referenced value.

For indexed assignment:

obj.PropName(n) = val;

MATLAB:

• Invokes the get method to get the property value
• Performs the indexed assignment on the returned property
• Passes the new property value to the set method

[Image Analyst]

I don't understand the question. In essence you say you want to "detect the index/position of the setted value" but then you say you did this:

obj.Prop(idx) = val;

so is idx NOT the index/position of the value you wanted to set? You already know this index value or else you could not have used it like that. So why do you think you need to "detect" it?

[Konrad Warner]

Yes a little difficult to explain.

Because Prop is stored in a static data object, an external class of properties that are shared among instances of the class that calls

obj.Prop(idx) = val; 

or rather:

obj.StaticData.Prop(idx) = val;

So the array gets 'filled' from a certain number of existing objects during runtime. The index - like a instance ID - is known but should trigger some calculations on the hole array as soon as its value gets passed in.

But maybe you are right. I can just can use a normal class method rather then a setter method inside the static data object and pass in both, value and idx.

Answer 1

[Tommy]

"For indexed assignment:

obj.PropName(n) = val;

MATLAB:

• Invokes the get method to get the property value
• Performs the indexed assignment on the returned property
• Passes the new property value to the set method"

If I am understanding this correctly, then

obj.PropName(n) = val;

is essentially similar to

myProp = obj.PropName; % get method
myProp(n) = val;
obj.PropName = myProp; % set method

so that neither the get method nor the set method ever sees n.

You could compare obj.Prop to val within your set method before you set obj.Prop so that you can determine which value is being changed, but that doesn't seem like a very good solution. You could also look into overloading subsasgn for your object, which might do the trick (requiring that you explicitly call subsasgn within your class rather than use '()' and '.', see here for explanation). Though I hope I'm overlooking a simpler solution.

[Konrad Warner]

Yes thanks, essentially I wanted to find n inside the setter method and your explanation made it more clear to me how these mehods handle arrays... even though it doesn't seem posible directly for setters there should be some workarounds for me