[bug #55810] sizeof() and whos() returns 0 bytes for classdef objects

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Follow-up Comment #11, bug #55810 (group octave):

Thanks for the review Markus.

I've attached a patch that fixes the identation issue, and also uses
Octave-specific syntax (with commenting conventions).

Your `dependent_prop` class fails because the `set` method shouldn't actually
set a dependent property. I think it's worth consulting the MATLAB
documentation for how Dependent properties are supposed to be used:
https://www.mathworks.com/help/matlab/matlab_oop/access-methods-for-dependent-properties.html.

Here's a slightly tweaked classdef that illustrates the same idea:

classdef dependent_prop < handle
  properties
    a = uint8(1)
  end
  properties (Dependent)
    b
  end

  methods
    function value = get.b(this)
      value = this.a + 5;
    end
  end
end


In your example, since `dependent_prop` is a handle class, then the size of
the machine word is returned by a `sizeof(dependent_prop)` call (8 bytes if
you're on a 64-bit computer).

If `dependent_prop` is a value class, then


>> dependent_prop
ans =

  1x1 dependent_prop object with properties:

      a: 1
      b: 6

>> sizeof(dependent_prop)
ans = 1


so yes, the size of the dependent property is not calculated in the size.
That's because the dependent property is not actually stored in the underlying
`octave_scalar_map` structure, which is what's used to compute the byte size
of a classdef.

No idea about MATLAB compatibility in this case, but because `sizeof` is very
much about the implementation of Octave internals, I don't think it really
matters in this case.

This patch can be pushed to the dev branch if you're not confident about
pushing it to stable.



(file #58443)

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