Pastable version of Method Hooks in Ruby: any cleaner?

<pre class='prettyprint' language='ruby'>#
# Project:: Ruby-Snippets
# 
# Author:: Christoph Heindl  (mailto:christoph.heindl@gmail.com)
# Homepage:: http://cheind.blogspot.com
#
# == Overview
# 
# Implements &lt;tt&gt;FollowingHook#following&lt;/tt&gt;. A
# utility to hook into instance methods and execute
# custom code after hooked methods are called.
#
# See discussion at
# http://cheind.blogspot.com/2008/12/method-hooks-in-ruby.html
#

# Contains methods to hook method calls
module FollowingHook
  
  module ClassMethods
    
    private
    
    # Hook the provided instance methods so that the block 
    # is executed directly after the specified methods have been invoked.
    #
    # There can only be one hook for a single instance method. Further attempts
    # to hook already hooked methods will be silently ignored.
    #
    # +syms+ is list of method symbols or stringified names to hook on
    # +block+ is the block to execute after hooked method has been invoked.
    # Block will receive two arguments: the receiver of the method and an argument hash
    # which contains the invoked method name &lt;tt&gt;:method&lt;/tt&gt;, the arguments passed to
    # the method &lt;tt&gt;:args&lt;/tt&gt; and the return value of the method &lt;tt&gt;:return&lt;/tt&gt;.
    #
    #   class Object
    #     include FollowingHook
    #     following :system do |receiver, args|
    #       p &quot;#{args[:method]} called with arguments #{args[:args].join(&quot;,&quot;)}&quot;
    #       p &quot;return value was #{args[:return]}&quot;
    #     end
    #   end
    #
    #   system('ruby --version')
    #   # =&gt; ruby 1.8.6 (2008-08-11 patchlevel 287) [i386-mswin32]
    #   # =&gt; &quot;system called with arguments ruby --version&quot;
    #   # =&gt; &quot;return value was true&quot;
    #   # =&gt; true
    #
    def following(*syms, &amp;block)
      syms.each do |sym| # For each symbol
        str_id = &quot;__#{sym}__hooked__&quot;
        unless private_instance_methods.include?(str_id)
          alias_method str_id, sym        # Backup original method
          private str_id                  # Make backup private
          define_method sym do |*args|    # Replace method
            ret = __send__ str_id, *args  # Invoke backup
            block.call(self,              # Invoke hook
              :method =&gt; sym, 
              :args =&gt; args,
              :return =&gt; ret
            )
            ret # Forward return value of method
          end
        end
      end
    end
  end
  
  # On inclusion, we extend the receiver by the defined class-methods
  # This is an ruby idiom for defining class methods within a module.
  def FollowingHook.included(base)
    base.extend(ClassMethods)
  end
end</pre>
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Pastable version of Method Hooks in Ruby: any cleaner?