Re: Change/add symbol for omitted default arguments?

[Jaroslav Hajek]

On Thu, Jul 29, 2010 at 3:29 AM, Judd Storrs <address@hidden> wrote:
> Octave allows default values for function arguments such as
> function [a,b,c] = myfunc(d,e=3,f)
>     ....
> endfunction
> When calling the function the default parameter can be used by entering the
> ":" symbol.
> [a,b,c] = myfunc(3,:,5)
> http://www.network-theory.co.uk/docs/octave3/octave_104.html
> Recent versions of octave (and Matlab apparently) have adopted ~ to mark
> ignored output parameters. Given this change I think it would be
> congruous for the octave language to also adopt the ~ for omitted default
> input arguments.
> [a,~,b] = myfunc(3,~,5)
> An alternative would be to allow : to also mark ignored output parameters.
> [a,:,b] = myfunc(3,:,5)
> "~" carries the meaning of "not" in octave and seems semantically more
> correct than ":" which carries the meaning "all".
>
> --judd
> [According to comments on StackOverflow Matlab additionally uses ~ inside
> function declarations to mark positional parameters that are ignored by the
> function definition.

Octave supports this as well.

> I'm not entirely sure what this achieves due to the
> copy-on-write parameter passing except that perhaps Matlab may be able to
> skip evaluating the arguments. I don't think that particular optimization
> can play nice with octave's evaluation model which allows things like
> myfunc(3,f=myfunc2(g=5),5) with the second parameter marked ~ in the
> function definition]
>

I wondered the same thing. It seems just syntactic sugar to cleanly
mark a placeholder input argument.

regards

-- 
RNDr. Jaroslav Hajek, PhD
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz