From: Alan Chen <alan@...>
Date: 2002-05-23T09:24:45+09:00
Subject: Re: confused about access control

On Thu, May 23, 2002 at 08:43:09AM +0900, Ian Macdonald wrote:
> Hi,
> 
> I'm rather confused about access control. Observe this:
> 
> irb(main):001:0> class String
> irb(main):002:1>   protected
> irb(main):003:1>   def undot!
> irb(main):004:2>     sub!(/^\.\./, '.')
> irb(main):005:2>   end
> irb(main):006:1> end
> nil
> irb(main):007:0> class Foo
> irb(main):008:1>   foo = '..123'
> irb(main):009:1>   foo.undot!
> irb(main):010:1> end
> NameError: protected method `undot!' called for "..123":String
>         from (irb):9
> 
> Why does this fail?
> 
> The pick-axe book says:
> 
> "Protected methods can be invoked only by objects of the defining
> class and its subclasses."
> 
> Well, foo is an instance of String, which is the class that defines
> the undot! method, so why does this not work?

foo is an instance of String, but Foo isn't a subclass of String.
Even if Foo were a subclass of String, foo.undot! is trying to publically
access the undot! method.

class Bar < String
  def undot_twice
    self.undot!.undot!
  end	
end

bar = Bar.new('....123')
bar.undot_twice => '123'

-- 
Alan Chen
Digikata LLC
http://digikata.com