gistfile1.rb

class RemoveMethodHook < Exception; end
class Module
  def before_method(name, &new_method)
    raise ArgumentError unless block_given?

    old_method = instance_method(name) rescue nil
    # new_method = Proc.new

    unless old_method.nil?
      define_method(name) do |*args|
        begin
          # module_exec(*args, &new_method) #
          new_method.call(self, *args)
        rescue RemoveMethodHook
          define_method(name, old_method)
        end

        old_method.bind(self).call(*args)
      end
    else
      define_method(name) do |*args|
        begin
          # module_exec(*args, &new_method) #
          new_method.call(self, *args)
        rescue RemoveMethodHook
          remove_method(name)
        end

        nil
      end
    end
  end

  def after_method(name, &new_method)
    raise ArgumentError unless block_given?

    old_method = instance_method(name) rescue nil
    # new_method = Proc.new

    unless old_method.nil?
      define_method(name) do |*args|
        ret = old_method.bind(self).call(*args)

        begin
          # module_exec(*args, &new_method) #
          new_method.call(self, *args)
        rescue RemoveMethodHook
          define_method(name, old_method)
        end

        ret
      end
    else
      define_method(name) do |*args|
        begin
          # module_exec(*args, &new_method) #
          new_method.call(self, *args)
        rescue RemoveMethodHook
          remove_method(name)
        end

        nil
      end
    end
  end
end