On Thu, 11 Apr 2002, Piers Cawley wrote:
> "Miko O'Sullivan" <[EMAIL PROTECTED]> writes:
> > The current plans indicate that a subroutine's params should be defaulted
> > like this:
> >
> > sub load_data ($filename ; $version / /= 1) {...}
> >
> > (The space between / and / is on purpose, my emailer has problems if
> > they are together.) If that's the technique, how does the caller
> > indicate that the second param is *supposed* to be undef? If I were
> > to call a sub like this:
> >
> > load_data ($filename, undef);
> >
> > then I would expect that means that I am explicitly saying the
> > second argument is supposed to be undef. However, if I call it like
> > this:
> >
> > load_data ($filename);
> >
> > then I'm not sending the second param and it can be whatever the
> > default is. Ergo, I propose that / /= and simply = are both allowed
> > and mean slightly different things:
> >
> > # $version is 1 if the second param isn't sent at all
> > sub load_data ($filename ; $version = 1) {...}
> >
> > # $version is 1 if the second param is undef
> > sub load_data ($filename ; $version / /= 1) {...}
> >
> > (Yes, this is a repeat of an earlier suggestion. It was suggested I might
> > repost reworded.)
>
> I think you're right that this is a valid distinction, I'm just not
> sure if it's not a little too subtle and that the two different
> notations won't cause confusion. I *think* that the //= case is going
> to be the more common one, and one could always handle the first case
> more explicitly by doing:
>
> sub load_data ($filename; $version) {
> $version = 1 if @_.length < 2;
> ...
> }
>
> Yes, it is undoubtedly uglier, but I don't think it's a common enough
> case that that worries me.
Indeed, and with the //= thing, you can let parameters in the middle
default. The only other language that lets you do that is VB, and I
actually kinda liked it. (Not insinuating that VB is actually a language
or anything...)
Luke
