From: nobu.nokada@...
Date: 2005-04-12T08:32:27+09:00
Subject: Re: Factory design

Hi,

At Tue, 12 Apr 2005 06:56:09 +0900,
Claus Spitzer wrote in [ruby-talk:137841]:
> A friend of mine has recently started using Ruby, and has run into a
> little problem. He is trying to create different objects depending on
> the contents of a string. His intuition is to use factory design for
> this, and he'd like to know if there is a Ruby Way to do this.

I remember that I'd written this library and posted somewhere
once.


module Factory
  def factory(c = Proc.new)
    (@__factory ||= []) << c
  end

  def create(*args)
    n = args.size
    @__factory.reverse_each do |f|
      next if (a = f.arity) < 0 ? n < ~a : n != a
      return f if f = f.call(*args)
    end if defined?(@__factory)
    nil
  end

  def inherited(klass)
    factory(klass.method(:create))
    super(klass)
  end
end

if $0 == __FILE__
  class A
    extend Factory

    def initialize(obj)
      @obj = obj
    end

    factory(method(:new))
  end

  class B < A
    factory do |obj|
      new(obj) if obj.respond_to?(:split)
    end
  end
  class B1 < B
    factory do |obj|
      new(obj) if obj.respond_to?(:string)
    end
  end
  class C < A
    factory do |obj|
      new(obj) if obj.respond_to?(:readline)
    end
  end

  p A.create("")
  require 'stringio'
  s = StringIO.new
  p A.create(s)
  p B.create(s)
end


-- 
Nobu Nakada