From: Joel VanderWerf <vjoel@...>
Date: 2002-09-12T06:58:26+09:00
Subject: Re: Multimethods (was Re: Larry Wall's comments on Ruby)

Christoph wrote:
> "Joel VanderWerf"  wrote
> ....
> ....
> 
>>Without changing Ruby internals, what about something like:
>>
>>
>>module Physics
>>
>>   Collide = GenericFunction.new {|actor, object, *args|}
> 
> 
> Nice!  ... additionally one could also explicitly specify the
> number of  ``dispatch-relevant arguments ?

I was assuming that the gf would always dispatch on the non-* arguments, 
and just pass on the rest to the method that it selects, but maybe that 
would be the default behavior, and your suggestion below could override 
the default.

>      Collide = GenericFunction.new(2) {|actor, object, *args|}

The member method is, of course, free to be more explicit about these 
args, as in

   Physics::Collide.add_method Ship, Ship do |ship, other_ship, notify|
     ...
     notify.call("You are now an ex-parrot.")
   end

The notify argument is not required when rocks collide with each other, 
and so there is no need to specify it in the gf arguments.

>>   #
>>   # The generic function will dispatch on actor and object, but
>>   # simply pass args to the selected method.
>>   #
>>   # The distinction in the block can be detected by checking whether #arity
>>   # returns 3 or -3.
>>   #
>>
>>end