require "active_support/concern" module Rails class Railtie module Configurable extend ActiveSupport::Concern module ClassMethods delegate :config, to: :instance def inherited(base) raise "You cannot inherit from a #{superclass.name} child" end def instance @instance ||= new end def respond_to?(*args) super || instance.respond_to?(*args) end def configure(&block) class_eval(&block) end protected def method_missing(*args, &block) instance.send(*args, &block) end end end end end