Re: nthoutarg function?

[Jordi Gutiérrez Hermoso]

2011/10/14 John W. Eaton <address@hidden>:
> On 14-Oct-2011, Jordi Gutiérrez Hermoso wrote:
>
> | This blog post got me thinking:
> |
> |     http://abandonmatlab.wordpress.com/2010/05/28/multiple-output-arguments/
> |
> | The blogger is quite right that multiple output arguments are a
> | problem. They require temporaries, and this makes for some slightly
> | brittle code.
> |
> | It's not difficult to implement a generalisation of the
> | "2nd_output_of" function:
> |
> |     function out = nthoutarg(fun, n, varargin)
> |       outargs = cell (1,n);
> |       [outargs{1:end-1}, out] = fun (varargin{:});
> |     endfunction
> |
> | Should this function be part of Octave? I'm all for prettifying the
> | language as much as possible.
>
> Because the value of nargout can change the behavior of a function,
> you might need to specify the number of the argument you want and
> the value of nargout to pass to the function separately. For
> example, when calling functions like svd. With your definition of
> nthoutarg,
>
>  nthoutarg (@svd, 2, rand (3, 4))
>
> fails.  You need something like
>
>  function out = nthoutarg (fun, n, nout, varargin)
>    if (nargin > 2 && nout >= n)
>      outargs = cell (1, nout);
>      [outargs{:}] = fun (varargin{:});
>      out = outargs{n};
>    else
>      print_usage ();
>    endif
>  endfunction

Right, something like it, except it would be nice to make nout == n by
default. I think you would have to change the order of the arguments,
so that

    nthargout(n, nout, @fun, args{:})
    nthargout(n, @fun, args{:})

could be the two calling forms.

Is this function worth it?

- Jordi G. H.