Damian Conway <[EMAIL PROTECTED]> writes:
> Richard Proctor asked:
>
> > If one has a simple sub such as factorial:
> >
> > sub factorial(int $a) {...}
> >
> > then one subsequently declares the multi form of factorial to pick up the
> > non-integer form:
> >
> > multi factorial(num $a) {...}
> >
> > Does this promote the original declaration of factorial to a multi?
> > if not what happens?
>
> What happens is that the subroutine hides the multimethod
> (thoroughout the subroutine's package).
>
> We didn't include it in A6 but our current notions (i.e. this week ;-)
> about interactions between subs, methods, and multimethods are
> something like this:
>
> Dispatched to first existing
> Call and visible of...
> ==================== ============================
>
> foo($x, $y); 1. C<sub DISPATCH>
> 2. C<multi DISPATCH>
> 3. C<sub foo>
> 4. C<sub AUTOLOAD>
> 5. C<multi foo>
> 6. C<multi AUTOLOAD>
>
>
> Invocant.foo($x, $y) 1. C<method Invocant::DISPATCH> or inherited
> 2. C<multi DISPATCH>
> 3. C<method Invocant::foo> or inherited
> 4. C<method Invocant::AUTOLOAD> or inherited
> 5. C<multi foo>
> 6. C<multi AUTOLOAD>
This looks like a classic Chain of Responsibility pattern. I wonder,
would it be possible to expose the dispatch system as an object
(chain) which could be modified by the courageous programmer so that
one could, for instance, set up a different dispatcher for the rest of
a lexical scope which dispatched to multimethods before subs/methods?
I know you could override it by implementing your own DISPATCH sub,
but an OO interface does have a certain appeal to it. Hell, one could
probably implement a suitable DISPATCH sub that would look for a
$*DISPATCHER and dispatch via that if it existed or just do a NEXT
call if it didn't. Something like this might do the trick:
sub DISPATCH {
if (defined $*DISPATCH) {
$*DISPATCHER.dispatch(@_);
}
else {
NEXT(@_);
}
}
So, even if there isn't a 'core' way of manipulating the current
dispatcher it's possible to write a module that would make it look
like you could.
Sometimes I scare myself.
--
Piers
