Example of overloading times operator doesn't work

I work out on one example in Matlab documentation showing application of subclasses of built-in types. In the example, DocUint8 class is derived from uin8 class and overrides its times operator. For some reasons, I couldn't get the overload function for this specific times operator work. As the below code points out, it is expected that the overloading operator should return an object of DocUint8 type, but instead I always get returned object of uint8 type. The strange thing is that my attempt to overload other operators such as "plus", "minus", "transpose", etc. all seem having no such problem (returned object is of subclass type). In addition, when setting breakpoint in the code, I don't see the debugging stops in the overloading method for this times operator. I did also try to clear all classes and clear all as well as restarting Matlab multiple times but none of those did work for me. Can someone explain to me if there's anything I have missed? Thanks!

classdef DocUint8 < uint8
   methods
      function obj = DocUint8(data)
         if nargin == 0
            data = uint8(0);
         end
         obj = obj@uint8(data); % Store data on superclass
      end
      function h = showImage(obj)
         data = uint8(obj);
         figure; colormap(gray(256))
         h = imagesc(data,[0 255]);
         axis image
         brighten(.2)
      end
      function o = times(obj,val)
        u8 = uint8(obj).*val; 
        o = DocUint8(u8);
      end
   end
end

This is what I get after multiplying the obj img1. I expect the returned obj should also be of type DocUint8.

>> img1 = DocUint8(rand(3)*255)

img1 = 

  3x3 DocUint8:

  uint8 data:
  150  120   50
   53   59   58
   77  215   44

>> img1*2

ans =

  255  240  100
  106  118  116
  154  255   88

Answer 1

[Steven Lord]

The * operator corresponds to the mtimes function. The operator for the times function is .* with the period in front.

img2a = img1*2 % uint8
img2b = img1.*2 % DocUint8

See the table at the end of this documentation page for a list of which functions correspond to which operators.

You should also modify your times method so that it doesn't assume the DocUint8 object is the first input. In the expression A.*B at least one of A and B must be an instance of the DocUint8 class, but it doesn't necessarily have to be A. Your code currently does not handle this case:

img3 = 2.*img1 % errors