[Octave-bug-tracker] [bug #43813] Edge case in indexing rules does not work as in Matlab

[jose]

URL:
  <http://savannah.gnu.org/bugs/?43813>

                 Summary: Edge case in indexing rules does not work as in
Matlab
                 Project: GNU Octave
            Submitted by: josombio
            Submitted on: Sat 13 Dec 2014 15:19:12 GMT
                Category: Interpreter
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: José
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.8.2
        Operating System: GNU/Linux

    _______________________________________________________

Details:

There as an edge case in indexing rules that is not handled as in Matlab. This
case is not officially documented in Matlab, but unofficially here
<http://stackoverflow.com/questions/4895556/how-to-wrap-a-function-using-varargin-and-varargout>
by SCFrench, an employee from The Mathworks.

According to SCFrench, the rule is (literaly):

When performing subscripted assignment, if
* subscripted-assigning to an uninitialized variable, AND
* the uninitialized variable is curly-brace indexed, AND
* the index in the curly braces is empty, AND
* the left-hand side appears inside square braces, AND
* the right-hand side resolves to a value / returns an output
Then the uninitialized variable is assigned a scalar cell  containing the
value returned by the right-hand side.

The test: the following code, executed in Matlab

>> clear uninit % just to make sure uninit is uninitialized
>> [uninit{[]}] = sin(0)
uninit = 
    [0]

and in Octave 3.8.2

octave:142> clear uninit %
octave:143> [uninit{[]}] = sin(0)
uninit = {}(0x0)


This produces that the following function wrapper

function varargout = wrapper( varargin )
[varargout{1:nargout}] = someFunction( varargin{:} ); 
endfunction

does not return in Octave a result when the wrapper is called with no output
arguments when someFunction returns something even if no output arguments are
requested. This is shown in the following code

> [varargout{1:nargout}] = sin( varargin{:} );
> endfunction
octave:76> wrapper(0) %this should give ans = 0, and it does not.
octave:77> a=wrapper(0)
a = 0
octave:78> sin(0)
ans = 0 






    _______________________________________________________

Reply to this item at:

  <http://savannah.gnu.org/bugs/?43813>

_______________________________________________
  Message sent via/by Savannah
  http://savannah.gnu.org/