[Octave-bug-tracker] [bug #60181] Incompatibilities with set methods of classdef handle classes

[Markus Mützel]

URL:
  <https://savannah.gnu.org/bugs/?60181>

                 Summary: Incompatibilities with set methods of classdef
handle classes
                 Project: GNU Octave
            Submitted by: mmuetzel
            Submitted on: Sat 06 Mar 2021 02:17:37 PM CET
                Category: Interpreter
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: dev
         Discussion Lock: Any
        Operating System: Any

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Details:

In bug #60143, the following behavior of classdef set-methods was observed
with the attached classes in Matlab R2020b:

>> a = bug60143_value;
>> a.t = 4
The set function for property 't' must return an instance of class
'bug60143_value'.

>> a.u = 3
method set.u

a =

  bug60143_value with properties:

    t: []
    u: 3

>> b = bug60143_handle;
>> b.t = 2
method set.t
In set function for property 't', the class of the output object is 'double';
the class of the input object is 'bug60143_handle'. They should be the same.

>> b.u = 4
method set.u

b =

  bug60143_handle with properties:

    t: []
    u: 4


The syntax highlighter in its editor marks the set function for u in class
`bug60143_value` with an error highlight "Set Methods must have at most one
output.". But -- surprisingly -- it still seems to work (ignoring the extra
output).

It looks like it is possible that a set function of a handle class returns a
different instance of the same class. That's interesting. I didn't know this
was possible.

With Octave 7 (hg id 65979d33f147), I see the following:

>> a = bug60143_value;

>> a.t = 4

error: set.t: function called with too many outputs
error: called from
    set.t
>> a.u = 3

method set.u
a =

  bug60143_value object with properties:

      t: [0x0 double]
      u: [1x1 double]

>> b = bug60143_handle;

>> b.t = 2

method set.t
b =

  bug60143_handle object with properties:

      t: [1x1 double]
      u: [0x0 double]

>> b.u = 4
[snip]
method set.u
method set.u
method set.u
method set.u
method set.u
method set.u
method set.u
error: max_recursion_depth exceeded
error: called from
    set.u
    set.u at line 21 column 11


The results with the value class look like they are compatible.

But the behavior of the handle class is different:
It looks like we should not discard the return value of the set-method. One
return value seems to be ok. But the type of the return value must match the
class.
Additionally, it looks like a set-method should not be able to call itself
even if the used object is a different instance of the same class (or whatever
the exact condition is).



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File Attachments:


-------------------------------------------------------
Date: Sat 06 Mar 2021 02:17:37 PM CET  Name: bug60143_value.m  Size: 270B  
By: mmuetzel

<http://savannah.gnu.org/bugs/download.php?file_id=51009>
-------------------------------------------------------
Date: Sat 06 Mar 2021 02:17:37 PM CET  Name: bug60143_handle.m  Size: 348B  
By: mmuetzel

<http://savannah.gnu.org/bugs/download.php?file_id=51010>

    _______________________________________________________

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