> MyDumbClass has no subsasgn: isn't that involved in making this work?

It shouldn't be. There should be a default implementation that works like it does for structs. Overriding subsasgn and related methods should only be necessary if you have a custom internal array representation, for example, if you're writing a planar-organized object.

> 2. How do you know its not a problem with your `packajoozle` class?

The PkgVer class is very simple. But, valid question.

Here's a simpler reproduction case. I have a MyDumbClass.m, the entirety of which is this:

classdef MyDumbClass

  properties
    x = 42;
  endproperties

endclassdef

Same behavior:

>> x = MyDumbClass
x =
<object MyDumbClass>

>> xx = x;
>> xx(2) = x;
>> xx(3) = x;
>> xx(2) = []
error: cannot convert `null_matrix' into `object'
>>

The special 'x(ix) = []' syntax is supposed to remove identified elements from the array x, regardless of x's type. That is, [] may be a double, but it doesn't matter whether x's type is assignment-compatible with double for this special calling form.

This doesn't work for classdef objects. For example:

octave:1> addpath('~/local/repos/octave-packajoozle/inst')
octave:2> pkg = packajoozle.internal.PkgVer ('financial', '0.5.3')
pkg =
financial 0.5.3

octave:3> p = pkg;
octave:4> p(2) = pkg;
octave:5> p(3) = pkg
p =
financial 0.5.3; financial 0.5.3; financial 0.5.3

octave:6> p(2) = []
error: cannot convert `null_matrix' into `object'
octave:6>