How to generate code for a class subclassing a built-in class?

Hi,

I'm trying to generate code for this example (class and test function in two separate .m-files):

%#codegen
classdef DocSimpleDouble < double
   methods
      function obj = DocSimpleDouble(data)
         obj = obj@double(data); % initialize the base class portion
      end
   end
end

function r = test_doc
d = DocSimpleDouble(5);
e = DocSimpleDouble(6);
r = d + e;

Trying this

codegen -c -config:lib test_doc.m

I get this error message:

??? Base class 'double' cannot be loaded.

Error in ==> DocSimpleDouble Line: 4 Column: 7
Code generation failed: Open error report.
Error using codegen

I did not see anything in the docs that subclassing a built in class is not possible with code generation.

Any ideas?

Thank you!

Tilo