Monkey patch by prepend

monkey-patch-by-prepend.rb

class A
  def hi
    puts 'hi'
  end
end

a = A.new
a.hi
# => "hi"

module M1
  def hi
    puts 'hi in M1'
    super
  end
end

A.send :prepend, M1
a.hi
# => "hi in M1"
# => "hi"

class A
  def hi
    puts 'hi redefined'
  end
end

a.h
# => hi in M1
# => hi redefined