How do I enable subscripting in a custom class inhereting uint64

Apologies if this is a simple question; I'm new to OOP with Matlab.

I'm using Matlab 8.0.0.783 (R2012b) on a PCWIN64.

I'd like to enable subscripting in a custom class inheriting uint64. For example:

classdef TestClass < uint64
    properties
        prop
    end

      methods
          function obj = TestClass(val)
              obj = obj@uint64(val);
          end

          function ret = subsref(self, S)
              ret = builtin('subsref', self, S);
          end
      end
  end

Assuming the above is saved to a file TestClass.m in the current path, when I execute the following in the command window

A = TestClass([4, 5, 6]);
B = A(1)

the variable B contains the entirety of A, and not just 4 as I would desire. Not surprisingly, if I execute A(2), I receive an "Index exceeds..." error:

Error using subsref
Index exceeds matrix dimensions.

Error in TestClass/subsref (line 13)
            ret = builtin('subsref', self, S);

In place of the "builtin" line, I have also tried:

subsref@uint64(self, S)  % (1)
subsref(self, S)         % (2)
self(S.subs{1})          % (3)

(1) returns the "subsref overloading necessary" error:

Cannot use '(' or '{' to index into an object of class 'TestClass' because 'TestClass' defines properties and subclasses 'uint64'.

Click here for more information.

      Error in TestClass/subsref (line 14)
                  ret = subsref@uint64(self, S);

(2) returns the recursion error:

Maximum recursion limit of 500 reached. Use set(0,'RecursionLimit',N)
to change the limit.  Be aware that exceeding your available stack space can
crash MATLAB and/or your computer.

Error in TestClass/subsref

(3) returns the entire object:

B = 

    TestClass

    Properties:
      prop: []

    uint64 data:
                      4                    5                    6

    Methods, Superclasses

None of the errors seem all that surprising. The behavior that is surprising me is that of the "builtin" command. It's as if the interpreter cannot find the subsref method of the bound uint64 object and is falling back by just returning the object itself?

My question is: Why doesn't the "builtin" code work here as I would expect? How would I go about subscripting the bound superclass within the subclass's subsref method?

Thanks in advance for your help!

Answer 1

[Philip Borghesani]

What is the purpose of prop? This class is index-able and works as a uint64.

 classdef tclass < uint64
      methods
          function obj = tclass(val)
              obj = obj@uint64(val);
          end
      end
 end

Once you add a property indexing into an overloaded base type becomes harder to define. Does you object contain a uint64 array and some other global description or should prop have the same dimensions as the data it holds? what is obj(1)?

One possible overly simplified solution for your class:

classdef tclass < uint64
  properties
      prop
  end
  methods
     function obj = tclass(val)
        obj = obj@uint64(val);
     end
     function ret = subsref(self, S)
         val=uint64(self);
         ret = val(S.subs{1});
     end
  end
end

If you want to use buitin to implement subsref try:

ret = builtin('subsref', uint64(self), S);

Answer 2

[Mike Stinger]

@Philip: Your solution worked perfectly! To my understanding, by "casting" the object as a uint64, you enabled indexing into (a copy's) contents. Fantastic! Thanks Philip!