From bug-octave-request at bevo dot che dot wisc dot edu Thu Jan 22 20:43:35 2004
Subject: unintended consequences of nargin changes
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Quentin Spencer <qspencer at ieee dot org>
Cc: bug-octave at bevo dot che dot wisc dot edu
Date: Thu, 22 Jan 2004 20:42:37 -0600

On 22-Jan-2004, Quentin Spencer <qspencer at ieee dot org> wrote:

| The recent changes to nargin in CVS broke code in the octave-forge 
| legend function that uses the syntax:
| nargin--
| This now gives the following result:
| error: evaluating postfix operator `--' near line 137, column 11
| 
| Replacing this statement with "nargin = nargin-1" works, but if this 
| syntax is used anywhere else, it will break.

Ugh.  I see that the Octave manual has some example code that
uses --nargin and nargin--, and nargin-- is used in three of Octave's
plotting functions.

To implement the new nargin and nargout functions, I introduced new
automatic variables, __nargin__ and __nargout__, so you could write

  __nargin__--;

Or, you could also write

  nargin = nargin ();

before anything else and then use

  nargin--;

but that is somewhat ugly as well (perhaps using a name different from
nargin for the variable would make it look better).

I don't think it will work to leave the old automatic variable names
in place, because then it won't work to write

  function foo ()
    nargin ('some_fun')
  endfunction

because if the automatic variables named nargin and nargout are
installed in the function symbol table, they will be found instead of
the nargin and nargout functions.

I'd be willing to undo this change, but then we will probably have
other people complaining about the incompatibility later.

Suggestions?

jwe



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
-------------------------------------------------------------