Using subsref on a class with a robust . operator?

Hi, I wanted to overload subsref in a class to use the {} notation to index a class property (obj.stimuli below):

classdef MyDataClass
  properties
    stimuli = []
    info = ''
  end
  properties (SetAccess = private)
    Date
  end
  methods
    function obj = MyDataClass()
      obj.stimuli = {'hickory';'dickory';'dock'};
      obj.info = 'example class';
      obj.Date = clock;
    end
    function sref = subsref(obj,s)
      switch s(1).type
        case '.'
          sref = builtin('subsref',obj,s);
        case '()'
          sref = builtin('subsref',obj,s);
        case '{}'
          sref = builtin('subsref',obj.stimuli,s);
      end
    end
    function testMe(obj)
      for i = 1:size(obj.stimuli,1)
        fprint('%s ',obj.stimuli{i});
      end
      printf('\n')
    end
    function out = mySize(obj)
      out = size(obj.stimuli,1);
    end
  end
end

However, the problem is that overloading the . operator causes problems because now unless every method returns a value (testMe doesn't, mySize does in the example), then subsref will fail:

>> m=MyDataClass

m =

MyDataClass

Properties:
  stimuli: {3x1 cell}
     info: 'example class'
     Date: [2012 8 30 18 3 40.5521]

Methods

>> m{1}

ans = hickory

>> m.info

ans = example class

>> m.mySize

ans = 3

>> m.testMe

Error using MyDataClass/testMe
Too many output arguments.

Error in MyDataClass/subsref (line 18)
          sref = builtin('subsref',obj,s);

What is the best way to handle this robustly? Having to parse each s.subs name to call builtin will fix this but is not very elegant and liable to break as the class grows. I basically need something like a varargout.

Answer 1

[Steve Edwards]

Hi Ian, It turns out that subsref does have a varargout signature (it's just not documented). Here's the function signature you want:

function varargout = subsref(obj,s)
    varargout{1:nargout} = builtin('subsref',obj,s);
end

You would probably want to make sure that '.' and '{}' use the varargout functionality, as they can both return comma separated lists. I'm also guess that you'll want to overload numel for your brace indexing.