From: Mike Austin <noone@...>
Date: 2006-03-21T15:08:50+09:00
Subject: Re: Method overload, care to improve?

Trans wrote:
> Thanks Andrew.
> 
> I'm afraid I don't care for how the strongtyping lib handles
> overloading with the #overload call internal to the method. It
> undermines dynamic capabilities. Eg.
> 
>      def bar(*args)
>          overload(args, String, String) {
>             | s1, s2 |
>             ...
>             return
>          }
> 
>          overload(args, String, Integer) {
>             | s, i |
>             ...
>             return
>          }
> 
>          overload_error args
>       end
> 
> It would be tricky to add another overload post defnition of the
> original.

I would agree.  You loose the most powerful part - to define methods after the 
definition.  One good example for multimethods are in event callbacks.  You can 
capture the event you want without a bunch of switch code:

overload :mouse_down, LeftButton, ButtonDown do |button, state, x, y|
   puts "left mouse button down"
end

Unfortunately it looks a bit odd.  If I was using it in a library internally it 
might be cool.  But exposing library users to it would be something else.  I 
wonder if it could be done like this:

class Test
   generic :foo

   def foo.Integer_String( x, y )
     return x * y
   end
end

t = Test.new
t.foo( 10, 20 )


Here's a prototype, but doesn't quite work:

def generic( symbol )
   class_eval do
     #instance_variable_set( "@@#{symbol.to_s}", Object.new )
     @@foo = Object.new
     define_method( symbol ) do | *args |
       # Find applicable method and call
       @@foo.Integer_String( *args )
     end
   end
end


Mike