around.rb

class Module
  def around_module
    unless defined? @around_module
      prepend (@around_module = Module.new)
    end

    @around_module
  end

  def around(&block)
    around_module.class_eval(&block)
  end
end

class String
  around do
    def reverse
      puts "before reversing"
      super
    end
  end
end

puts "hi".reverse