[Octave-bug-tracker] [bug #59737] end keyword not passed to oveloaded subsfef function within custom classdef

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?59737>

                 Summary: end keyword not passed to oveloaded subsfef function
within custom classdef
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Sun 20 Dec 2020 05:01:19 AM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: 6.1.0
         Discussion Lock: Any
        Operating System: Any

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Details:

= Problem Description =

The end keyword is not passed to an overloaded subsref function.

= How to reproduce =

Copy the following into cantuseend.m


classdef cantuseend
  properties
    value;
  endproperties
  methods
    function obj=cantuseend(a)
      obj.value=a;
    endfunction
    function obj=subsref(a,s)
      if strcmp(s.type,"()")
        obj=cantuseend(subsref(a.value,s));
        s
      else
        obj=builtin('subref',a,s);
      end
    endfunction
    function display(a)
      disp(a.value);
    endfunction
    function varargout=size(a,varargin)
      nout=nargout;
      if nout<=1
        varargout={size(a.value,varargin{:})};
      else
        varargout=nthargout(1:max(nargout,1),@size,a.value,varargin{:});
      end
    end
    function v=columns(a)
      v=columns(a.value);
    endfunction
    function v=rows(a)
      v=rows(a.value);
    endfunction
    function v=numel(a,varargin)
      v=numel(a.value,varargin{:});
    endfunction
    function v=ndims(a)
      v=ndims(a.value);
    end
    function v=length(a)
      v=length(a.value);
    end
  endmethods
endclassdef


At the command prompt type:

q=cantuseend(rand(4,1))
q(2:4)%works as expected
q(2:end)%Expected the above output got 1 by 0 empty result
q(end)%returns the first element not the last

I am printing what is in the sub-reference structure every time the function
is called. For the second call I get an empty subs for the third call I get
the number one within subs.

= Suggested Fixes =

Pass through a token which can be interpreted as end - even better if this
token can be interpreted by builtin functions.

Use the size method (or another method, document which one) of the classdef
object to convert end into the correct index. Give an error if the size method
has not been overloaded.

Raise an error telling the user end is not supported for custom objects and
tell the user to pass the last index of the object instead of end. This can't
currently be done within an overloaded subsref function as the input looks
valid. Without an error being thrown this bug could result in undetected
incorrect results and code that is very difficult to debug because without
looking at each output and finding this bug the code will look correct.







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