Dead simple model decorator base class

model_decorator.rb

require 'delegate'

# A suitable base class for defining a model decorator that automatically defines a model_klass
# singleton method, on all subclasses, that returns the model's class.
#
# Caveat: Your subclass name *must* match the following template: <code>"#{model_klass.name}Decorator"</code>
#
# - Example 1:  MyModelDecorator               # will decorate MyModel
# - Example 2:  MyNamespace::MyModelDecorator  # will decorate MyNamespace::MyModel
#
class ModelDecorator < SimpleDelegator

  # This is where the magic happens, albeit some very simple magic.
  # Whenever a subclass is declared, a suitable implementation of model_klass is automatically defined on it.
  def self.inherited(base)
    decorator_name = base.name.try(:dup) or raise TypeError, "anonymous ModelDecorator classes are not supported"
    decorator_name.sub!(/Decorator$/,'').present? or raise TypeError, "ModelDecorator subclass names must end with `Decorator'"
    base.module_eval "def self.model_klass; ::#{decorator_name} ; end"
    base.extend ClassMethods
  end

  module ClassMethods
    delegate :send, :public_send, :model_name, to: :model_klass
    
    def respond_to_missing?(symbol, include_private=false)
      model_klass.respond_to? symbol, include_private
    end
    
    alias_method :method_missing, :public_send
    private :method_missing
  end

  # :nodoc:
  def self.model_klass
    raise NotImplementedError, "subclasses must implement `model_klass`\n\nDid you, perhaps, redefine `model_klass' to call super?"
  end  
end