From: nobu.nokada@...
Date: 2003-11-27T20:18:23+09:00
Subject: Re: Class#inherited, class definition and industry.

Hi,

At Tue, 25 Nov 2003 23:26:58 +0900,
Ceri Storey wrote:
> Am I correct in thinking that the #inherited method of the parent class
> is called *before* the body of the class is evaluated? 

Yes.  The end of definition cannot be determined in Ruby.

> If so, is there a more sensible way of working around this, than
> something like the following?

I thought of similar one formerly, and still haven't get better
one.

Well, how about #singleton_method_added, if you use particular
singleton method as the key?
# But note that Module#name is pre-defined method.

  class Builder
    @@registry = {}
    class << self
      def singleton_method_added(name)
        @@registry[send(name)] = self if name == :name
        super
      end

      def lookup(name)
        @@registry.fetch(name) do
          raise ArgumentError, "No such Class"
        end
      end

      def create(name, *args)
        lookup(name).new(*args)
      end
    end
  end

  class Moogle < Builder
    def self.name
      "moogle"
    end
  end

  Builder.create("moogle")

Or, if names are always class names in lower case, you can use
the names even in #inherited.

  class Builder
    @registry = {}
    class << self
      def inherited(c)
        @registry[c.name.downcase] = c
        super
      end

      def lookup(name)
        @registry.fetch(name) do
          raise ArgumentError, "No such Class"
        end
      end
  end

You can define Builder.name as returning lower case name and
use it too.

  class Builder
    @registry = {}
    class << self
      def name
        super.downcase
      end
      def inherited(c)
        @registry[c.name] = c
        super
      end
    end
  end

And another one, with http://nokada.jin.gr.jp/ruby/factory.rb

  require 'factory'

  class Builder
    extend Factory
  end

  class Moogle < Builder
    factory do |name, *args|
      new(*args) if /\Amoogle\z/ =~ name
    end
  end

  p Builder.create("moogle")

-- 
Nobu Nakada