Module#method_undefined

Invoked as a callback whenever an instance method is undefined from the receiver.

module Chatty
  def self.method_undefined(method_name)
    puts "Undefining #{method_name.inspect}"
  end
  def self.some_class_method() end
  def some_instance_method() end
  class << self
    undef_method :some_class_method
  end
  undef_method :some_instance_method
end

produces:

Undefining :some_instance_method