output.txt

Widget metaclass ancestors...
[Wrapper, Class, Module, Object, Kernel]
The 2 `new' methods get invoked...
Invoked Widget::new
Invoked Wrapper's new
The 2 `render_on' methods get invoked...
Invoked Wrapping's render_on
Invoked Widget#render_on

respect-new.rb

# An example to illiustrate that the super-and-extend method wrapping
# technique respects `new' methods defined on the wrapped class, provided
# that `super' is called.
#
# For information on the super-and-extend technique, see:
#  http://codefluency.com/articles/2009/01/03/wrapping-a-method-in-ruby/

# This is the class to wrap
class Widget

  # Example of a scenario where the target class' `new' method is defined,
  # and `super' is being used, to show invocation order.
  #
  # We don't really care about the *order* that the Wrapper's new (just
  # a hook to extend the instance) fires, the wrapper works as expected.
  #
  # Keep in mind overriding `new' is a fairly rare case.
  #
  def self.new
    puts "Invoked Widget::new"
    super
  end

  # The method we're targeting
  def render_on(document, options = {})
    puts "Invoked Widget#render_on"
  end

end

# Yeah, the name says it
module Wrapper
  
  # `super' here invokes Class#new
  def new
    puts "Invoked Wrapper's new"
    super.extend(Wrapping)
  end

  module Wrapping
    
    def render_on(document, options = {})      
      puts "Invoked Wrapping's render_on"
      super # Widget#render_on
    end
    
  end

end

Widget.extend(Wrapper)

puts "Widget metaclass ancestors..."
p (class << Widget; self;  end).ancestors

puts "The 2 `new' methods get invoked..."
widget = Widget.new

puts "The 2 `render_on' methods get invoked..."
widget.render_on(nil)