From help-octave-request at bevo dot che dot wisc dot edu  Fri Dec 11 13:29:41 1998
Subject: Feature request: optional arguments
From: Joao Cardoso <jcardoso at inescn dot pt>
To: help-octave <help-octave at bevo dot che dot wisc dot edu>
Date: Fri, 11 Dec 1998 19:29:21 +0000

Hi,

Whenever a script function has several optional arguments it's a pain to
write the script function and use it.

Suppose that I want to have a function

	foo (x,y,z)

where *any* argument can be optional! If some argument is not specified,
than a default would be supplied. The usual approach would be to
consider some magic number to mean "use the default"; one could use "0",
so

	foo(0,0,123)

would mean: use default value for x and y, and use "123" for z.
Of course every function must have its own magic number for defaults, as
"0" can be meaningful for some functions.

What I propose is that Octave parser accepts missing argument as valid,
but do not assign it: for example:

	foo(,,123)

would set z=123 and let x and y undefined. Then in the script file one
would just check for the existence of each argument:

	if (!exist("x"))
		x=11;
	endif
	...

without having to check for the multiple occurrence/combination of
arguments: each one would be checked individually.

Of course, one could also specify the defaults in the function
declaration:

	function o = foo(x=11, y=22, z=33)

but to be useful it should allow *any* missing argument, not as in C++.

But this is ask too much, I think that the first approach is enough, and
it still keeps compatibility with existing script files.

As a concrete example, think in the script function "axis", and that you
want to keep all axis in autoscaling mode *except*, say, ymin and ymax.

Comments?
Joao

---
Joao Cardoso                |   e-mail: jcardoso at inescn dot pt
INESC, R. Jose Falcao 110   |   tel:	+ 351 2 2094322
4050 Porto, Portugal        |   fax:	+ 351 2 2008487