MATLAB: Classdef get methods: allowing get indexing into an array of length either (1×1) or (Nx1).

Question

Hello all, I am trying to sort out an issue best shown in this MWE, where I have a property that may be a column vector, but is initialized with a single value.

classdef myClass
    properties 
        A (:,1) double = 0;
    end
    methods
        
    end
end

Now, lets say I want to index into myClass.A using B = myClass.A(indx). However, I want it so that if myClass.A is still a (1×1) I want to return the initial value, not an "Index exceeds array bounds" error.

I can picture doing this with a get method of the following form

        function out = get.A(indx)
           if numel(obj.A) == 1
               out = obj.A(1);
           else
               out = obj.A(indx);
           end
        end

However, this will clearly not work since (A) get methods are limitited to one input, and I need to pass "indx", (B) I don't pass an instance of the object to get.A, so it has no access, and (C) this would wind up being infinitely recursive if I was able to do it.

SO:

Is there a way to allow use of a single default value as the output of a property regardless of the requested index, if that property has not yet been overwritten with an Nx1 vector.

Cheers,

DP

Answer 1

You would need to overload subsref, e.g.,

methods
 function out=subsref(obj,S)
   if S(1).type=="." && S(1).subs{1}=="A" && numel(S)>1 
       
       out=obj.A(min(S(2).subs{1},1));
   else
       error 'Undefined Indexing'
   
   end
  end
end