Callbacks in pure ruby - prepend over alias_method

I had a need to encrypt a password before an object was saved.  I searched around to find a gem that implemented callbacks in ruby but didn't find much.  I did come across this stack over flow post with some good recommendations.  Using the magical method_added worked pretty well for a single module included into a class.  However it didn't work so well when I had multiple modules inside my gem that were included in a class.  The original code looked something like this:

	def method_added(method)
	if !setting_callback
	redefine_method(method) if is_a_callback?(method)
	end
	end
	def redefine_method(original_method)
	@setting_callback = true
	original = instance_method(original_method)
	define_method("#{original_method}_with_callbacks".to_sym) do |*args, &block|
	trigger_callbacks(original_method, :before)
	return_val = original.bind(self).call(*args, &block) if original
	trigger_callbacks(original_method, :after)
	return_val
	end
	alias_method original_method, "#{original_method}_with_callbacks".to_sym
	@setting_callback = false
	end

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This worked until I had a save method in my class and a save method in my module. The callback no longer worked.  The methods got stomped on when they were included.  So now onto the awesome prepend Module method.  This is a much cleaner way of prepending your module with an anonymous module that includes your method.  It is then properly in your call hierarchy so you can call it via super!

Here is what the callback code looks like now.  I feel like it is very readable and easy to comprehend:

	module CallbackPureRuby
	def self.included(klass)
	klass.extend ClassMethods
	klass.initialize_included_features
	end
	module ClassMethods
	def initialize_included_features
	@callbacks = Hash[:before, {}, :after, {}]
	class << self
	attr_accessor :callbacks
	attr_accessor :setting_callback
	end
	end
	def store_callbacks(type, method_name, *callback_methods)
	callbacks[type][method_name] = callback_methods
	if !setting_callback
	prepend_method(method_name)
	end
	end
	def method_missing(method, *args, &block)
	if method.to_s =~ /^before|after$/
	store_callbacks(method, *args)
	else
	super
	end
	end
	def prepend_method(original_method)
	@setting_callback = true
	save_with_callbacks = Module.new do
	define_method(original_method) do |*args, &block|
	trigger_callbacks(original_method, :before)
	return_val = super()
	trigger_callbacks(original_method, :after)
	return_val
	end
	end
	prepend save_with_callbacks
	@setting_callback = false
	end
	end
	def trigger_callbacks(method_name, callback_type)
	unless self.class.callbacks[callback_type][method_name].nil?
	self.class.callbacks[callback_type][method_name].each{ |callback| __send__ callback }
	end
	end
	end

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Feel free to post comments and feedback :)