From: Trans <transfire@...>
Date: 2006-09-29T02:45:29+09:00
Subject: Re: Multi-Module Alternative to the Factory Pattern?


ara.t.howard@noaa.gov wrote:
> why not:
> [snip]

Only becuase there are a lot of arguments to pass.

> btw.  for these kinds of setups: modules with state (singletons) i've been
> using prototypes lately:

Right on. I do like the prototype stuff. Just don't have the time to
invest init at them moment though.

[snip cool example use of prototype]

> i guess i'm failing to see what multi-module inclusion givs you that delegation
> plus argument passing (into the delegate module not the other way around)
> doesn't?

The advantage is access to the internal state --no passing of
attributes required. Esspecailly true when you have alot of
attributes/arguments involved. Simple example:

     require 'facet/kernel/as'

     module DEB
       A, B, C = %w( D E B )
       def pack_step_one() p A+a end
       def pack_step_two() p B+b end
       def pack_step_three() p C+c end
     end

     module RPM
       A, B, C = %w( R P M )
       def pack_step_one() p A+a+b+c end
       def pack_step_two() p B+b+c+a end
       def pack_step_three() p C+c+a+b end
     end

     class Packager
       include DEB, RPM
       attr :a,:b,:c
       def initialize
         @a,@b,@c = %w{ 1 2 3 }
       end
       def pack type
         as(type).pack_step_one
         as(type).pack_step_two
         as(type).pack_step_three
       end
     end

     packager = Packager.new
     packager.pack DEB, 42

     harp:~ > ruby a.rb
     "D123"
     "E231"
     "B312"
     42

Note #as works like #superior from my last example but uses magic-dot
notation to allow any method to be called. (It would be nice if it took
a block but I'll have to work on that).

T.