Monkeypatch - Illustrates how to re-open a class and redefine existing functionality

monkeypatch.rb

# define original class
class Example

  def say_hello
    puts "hello"
  end

end

# re-open the class and monkeypatch some of its existing functionality
class Example

  # re-define existing funnctionality
  def say_hello
    puts "hello from monkeypatch"
  end

end

# usage
Example.new.say_hello # => hello from monkeypatch