From: Ian Macdonald <ian@...>
Date: 2002-04-26T01:27:26+09:00
Subject: Re: appending methods to class inside module

On Thu 25 Apr 2002 at 16:44:57 +0900, Ed Sinjiashvili wrote:

> That's right, you define String class under Dog namespace - its fully
> qualified name is Dog::String.

Ah, OK. I was confused about the namespace issue.

> > My question is: how can I get String#bark to be defined, so that I can
> > then call the bark method on foo?
> Just define it at a toplevel.

OK, so now I have something like this:

class String
  def check
    if self.length > 2048
      puts "bad"
    else
      puts "good"
    end
  end
end

module Foo
  class Bar
    def initialize; end
    def baz
      "hello".check
    end
  end
end

include Foo

bar = Bar.new
bar.baz


This runs fine. However, the only thing that should be able to access
the new String#check method are objects of Class Bar.

Right now, I can add the following to the main namespace:

"goodbye".check

and it will execute correctly, but I don't want this. I would like
String#check to remain callable only for objects of type Foo::Bar.

I thought I could achieve this by declaring String#check to be
protected, since according to the Pickaxe book:

"Protected: Can be invoked only by objects of the defining class and
its subclasses."

Well, "hello" is of type String, which is the defining class of
String#check, so I expected to be able to call it. Instead, I get an
error:

./foo:19:in `baz': protected method `check' called for "hello":String (NameError)

I obviously don't understand protected and private methods very well
yet :-(

Any idea how I can restrict String#check so that it can only be called
by objects of Class Bar?

Ian
-- 
Ian Macdonald               | Your job is being a professor and
ian@caliban.org             | researcher: That's one hell of a good
                            | excuse for some of the brain-damages of
                            | minix. (Linus Torvalds to Andrew Tanenbaum)
                            |