Don't the Ruby methods instance_eval() and send() negate the benefits of private visibility?

Question

w = Widget.new # Create a Widget
w.send :utility_method # Invoke private method!
w.instance_eval { utility_method } # Another way to invoke it
w.instance_eval { @x } # Read instance variable of w

Looking at the example above which relates to the Widget class (below), the send and instance_eval methods violate all of the protections provided by private and protected visibility. If so, why bother with private and protected access in Ruby at all since there is no guarantee that your definitions will be honored?

class Widget
  def x # Accessor method for @x
   @x
  end
  protected :x # Make it protected
  def utility_method # Define a method
   nil
  end
  private :utility_method # And make it private
end

Answer 1

If you really want to protect instances of Widget, you can do this (and a bunch of other stuff; the code here is not a complete security solution, merely indicative):

class Widget

  def some_public_method
    ...
  end

  private

  def utility_method
    ...
  end

  def send(method, *args, &block)
    raise NotImplementedError.new('Widget is secure. Stop trying to hack me.')
  end

  def instance_eval(&block)
    raise NotImplementedError.new('Widget is secure. Stop trying to hack me.')
  end

  class <<self
    private
    def class_eval(&block)
      raise NotImplementedError.new('Widget is secure. Stop trying to hack me.')
    end
  end
end

Widget.freeze