プラギン形式のやつどう書こうみたいな

sample1.rb

module ShigotoMachine
  class Brain
    def initialize(adapter)
      @adapter = load_adapter(adapter)
    end
    
    def load_adapter(adapter)
      klass_name = sub(/\A./) { $&.upcase } # camelize
      result = [
        "shigoto_machine/adapters/#{adapter}", # bundled adapter
        "shigoto_machine-#{adapter}",          # external gem
      ].find do |f|
        begin
          require f
          true
        rescue LoadError => e
          false
        end
      end
      raise LoadError, "Can't load adapter \"#{adapter}\"" unless result
      Adapters.const_get(klass_name).new(self)
    end
  end

  module Adapters
    class Adapter
      def initialize(brain)
        @brain = brain
      end
    end

    # external file
    class DekiruHito < Adapter
    end
    
    # external file
    class Kuzu < Adapter
    end
  end
end

sample2.rb

module ShigotoMachine
  class Brain
    def initialize(adapter)
      @adapter = load_adapter(adapter)
    end
    
    def load_adapter(adapter)
      load_plugins unless @plugins_loaded
      Adapters.find(adapter).new(self)
    end
    
    def load_plugins
      # load shigoto_machine-* gems
    end
  end

  module Adapters
    def self.adapters
      @adapters ||= []
    end

    def self.register(name, klass)
      adapters[name.to_sym] = klass
    end

    def self.find(name)
      klass = adapters[name.to_sym]
      raise ArgumentError, "No such adapter \"#{name}\"" unless klass
      klass
    end

    class Adapter
      def initialize(brain)
        @brain = brain
      end
    end

    class DekiruHito < Adapter
      Adapters.register :dekiru, self
    end

    class Kuzu < Adapter
      Adapters.register :kuzu, self
    end
  end
end