[Octave-bug-tracker] [bug #54966] Error when assigning array to an object implementing subsasgn() subscripted using "{}"

[Martynas]

URL:
  <https://savannah.gnu.org/bugs/?54966>

                 Summary: Error when assigning array to an object implementing
subsasgn() subscripted using "{}"
                 Project: GNU Octave
            Submitted by: mpata
            Submitted on: Mon 05 Nov 2018 11:55:15 PM EET
                Category: Interpreter
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.4.1
        Operating System: Microsoft Windows

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Details:

GNU Octave seems to give an error message when assigning an array with several
elements to an object implementing subsasgn() method subscripted using curled
braces.

Let's say we have a class (implementing the same assignment for "()" and
"{}"):


classdef exampleclass

properties
  b = {1, 2};
end

methods
  function [obj] = exampleclass ()
  end
  
  function [varargout] = subsasgn (obj, IDX, RHS)
    switch IDX(1).type
      case '()'
        IDXcell = IDX;
        IDXcell(1).type = '()';
        [obj.b] = subsasgn (obj.b, IDXcell, RHS);
        varargout = {obj};
      case '{}'
        IDXcell = IDX;
        IDXcell(1).type = '()';
        [obj.b] = subsasgn (obj.b, IDXcell, RHS);
        varargout = {obj};
      otherwise
        [varargout] = {builtin('subsasgn', obj, IDX, RHS)};
    end
  end
end

end


And run a script trying out different assignments:


[ex] = exampleclass();

ex(1) = {2};
ex.b
ex{1} = {3};
ex.b
ex(1:2) = {2, 3};
ex.b
ex{1:2} = {3, 4};
ex.b


In GNU Octave the last assignment (but none of the previous ones) results in
error message (path removed):


ans =
{
  [1,1] =  2
  [1,2] =  2
}

ans =
{
  [1,1] =  3
  [1,2] =  2
}

ans =
{
  [1,1] =  2
  [1,2] =  3
}

error: invalid dot name structure assignment because the structure array is
empty.  Specify a subscript on the structure array to resolve.
error: called from
    examplescript at line 9 column 8
stopped in ...\examplescript.m at line 9
9: ex{1:2} = {3, 4};
                        ^


In Matlab assignments do not fail:


ans =

  1×2 cell array

    {[2]}    {[2]}


ans =

  1×2 cell array

    {[3]}    {[2]}


ans =

  1×2 cell array

    {[2]}    {[3]}


ans =

  1×2 cell array

    {[3]}    {[4]}





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