Re: varargout{:} = func() ?

[Ben Abbott]

On Wednesday, February 24, 2010, at 08:58AM, "Jaroslav Hajek" <address@hidden> 
wrote:
>On Wed, Feb 24, 2010 at 2:42 PM, Ben Abbott <address@hidden> wrote:
>> On Feb 24, 2010, at 12:03 AM, Jaroslav Hajek wrote:
>>
>>> On Wed, Feb 24, 2010 at 3:03 AM, Ben Abbott <address@hidden> wrote:
>>>> On Feb 23, 2010, at 8:11 PM, John W. Eaton wrote:
>>>>
>>>>> On 23-Feb-2010, Ben Abbott wrote:
>>>>>
>>>>> | On Feb 23, 2010, at 7:43 PM, WS wrote:
>>>>> |
>>>>> | > Has this notation been implemented in octave yet?
>>>>> | >
>>>>> | > Tx
>>>>> |
>>>>> | hmmm ... if you mean something like what is below, then yes.
>>>>> |
>>>>> | function varargout = foobar ( )
>>>>> |   for n = 1:numel(nargout)
>>>>> |     varargout{n} = n;
>>>>> |   end
>>>>> | end
>>>>> |
>>>>> | In this instance "varargout" has a special meaning.
>>>>> |
>>>>> | If you mean, something like what is below, then that doesn't work with 
>>>>> 3.2.x, but does with Matlab.
>>>>> |
>>>>> |     v{:} = {rand(1,2), rand(1,3)}
>>>>> |     error: invalid dimension inquiry of a non-existent value
>>>>> |
>>>>> | or
>>>>> |
>>>>> |     v{:} = rand(1,2)
>>>>> |     error: invalid dimension inquiry of a non-existent value
>>>>> |
>>>>> | Jarsolav, is this something that should be added to Octave?
>>>>>
>>>>> You need to write
>>>>>
>>>>> v = cell (expected_nargout, 1);
>>>>>
>>>>> [v{:}] = func (...);
>>>>>
>>>>> Does
>>>>>
>>>>> v = cell (expected_nargout, 1);
>>>>> v{:} = func (...);
>>>>>
>>>>> work in Matlab?  If so, I think that's a relatively new addition and
>>>>> in my opinion doesn't really fit with the rest of the language.
>>>>
>>>>>> v = cell (3, 1)
>>>> v =
>>>>    []
>>>>    []
>>>>    []
>>>>
>>>>>> v{:} = rand(1,2)
>>>> v =    [1x2 double]
>>>>
>>>> My impression is that this isn't very new, but as I've always found some 
>>>> of how Matlab handles cells to be counter intuitive (if not misleading), 
>>>> so I'm not in the habit of using this notation.
>>>>
>>>> Ben
>>>>
>>>>
>>>
>>> I'd even say this is a bug in Matlab. The LHS expression is obviously
>>> a cs-list with 3 elements, and it is outside multiple assignment, so
>>> it should give an error, like in Octave. This should only work if v is
>>> 1-by-1 (it does in Octave). What version of Matlab did you try?
>>
>> I tried R007b and R2009a. After some more experiments, it appears that 
>> Matlab assumes nargout = 1. Thus for ...
>>
>>        v{:} = func (...)
>>
>> The resulting cell is always 1x1.
>>
>> Ben
>>
>
>I think this is a Matlab bug and we should not reproduce it.
>Can you try the following in Matlab?
>
>v = cell (3, 1);
>v{1:3} = 1;
>
>s = struct ("x", {1, 2});
>s.x = 1;

I'm not taking a position on including this *feature*, but because of the 
number of times Mathworks has delibrately implemented a inconsistent *feature*, 
I'm skeptical that this is a bug :-(

    v = cell (3, 1);
    v{1:3} = 1
    ??? The right hand side of this assignment has too few values to satisfy
     the left hand side.

The following works.

    v(1:3) = {1}
    v =   [1]    [1]    [1]

For your second example, 

    s = struct ('x', {1, 2});
    s.x = 1;
    ??? Incorrect number of right hand side elements in dot name assignment.  
Missing []
    around left hand side is a likely cause.

Ben