なんとなく

gistfile1.rb

module Dispatchable
  def self.included(base)
    base.module_eval {
      def self.method_added(name)
        suffix = self.name.split("::").last.downcase
        return if name.to_s.end_with?(suffix)

        module_eval %{
          alias #{name}_#{suffix} #{name}
          undef #{name}
        }
      end
    }
  end

  def define_dispatch_rule(&block)
    __send__(:define_method, :dispatch_rule) do |target|
      block.call(target)
    end
  end

  def dispatch_methods(*methods)
    opts = ( methods.last.is_a?(Hash) ? methods.pop : { :default => :orig })

    methods.flatten.each do |method|
      default_method = [ method, opts[:default] ].join("_")
      if instance_methods.include?(method.to_sym) && !instance_methods.include?(default_method.to_sym)
        module_eval %{
          alias #{default_method} #{method}
        }
      end

      __send__(:define_method, method) do |*args|
        method_to_dispatch = [ method, dispatch_rule(self) ].join("_")
        method_to_dispatch = default_method unless respond_to?(method_to_dispatch)

        __send__(method_to_dispatch, *args)
      end
    end
  end
end