Re: Default arguments

[Søren Hauberg]

John W. Eaton skrev:
> Wouldn't it be better to have the syntax
>
>   function foo (arg = default_val)
Oh yes, very much! I just figured it would be harder to add such a change...

> As you note, there is the possiblity of a future incompatibility with
> Matlab.  Is this feature worth the risk?  I think I would want to use
> it in functions that are distributed with Octave to simplify code that
> needs to set default values.
As Tom noted, matlab will probably use the same syntax in the future (it 
is the defacto standard), so I think it's okay.

> | One thing that's missing from this idea, is a way to tell the function 
> | to use the default argument.
> My patch overloads ":" for this purpose:
> Is that reasonable?
I'm not sure. I think ":" is the obvious choice, but I do have one 
issue. Since matlab has decided to use "( )" to embreace function 
arguments AND index matrices it is hard to tell functions and matrices 
apart. One can think of functions as generalized matrices, so to some 
extend this choice is okay (I'm not a fan though). However, if we allow 
":" as an argument to a function it might be even harder to tell 
matrices and functions apart.

> Or, maybe what you really want is keyword arguments?  I think that
> would be harder to add.
Well, those would be nicer so you can avoid writing
  my_function(:,:,:,:,:,:, my_value)
which can be hard to read and instead write
  my_function(my_arg = my_value)
My original proposal was to just do something that was easy to 
implement, so I think it would be okay to not have keyword arguments.
Also, I don't think the ":" operator conflicts with keyword arguments, 
so that could be added later on.

> Although I've checked this patch in to the CVS archive, I consider it
> to be quite experimental.  If any nontrivial problems show up that are
> related to this change, I'll simply remove it.
I can't really test this until sometime next week (I have a hard 
deadline on monday), but then I'll report back...

Thanks,
Søren

P.S. Sometimes your abilities as a coding-ninja really impresses me...