Monkey patch by alias_method

monkey-patch-by-alias_method.rb

class A
  def hi
    puts "hi"
  end
end

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

module M1
  def self.included(base)
    base.send :alias_method, :hi_original, :hi
    base.send :alias_method, :hi, :hi_in_m1
  end

  def hi_in_m1
    puts "hi in M1"
  end
end

A.send :include, M1

a.hi
# => hi in M1
a.hi_original
# => hi