From: ara.t.howard@...
Date: 2006-07-26T15:32:48+09:00
Subject: Re: Automagic class prototyping

On Wed, 26 Jul 2006, Aleks Kissinger wrote:

> Anybody know any slick techniques for automatically prototyping
> classes so they can interact with each other in top-level code?  I've
> run through two methods, but I'm not real wild about either of them.
>
> Say for example, classes represent some security label and I want to
> allow things with one label to access those of another label.  So,
> these hypothetical classes all descent from Sec....
>
> class Sec
> class <<self
>  def allow(c)
>   (@allowed_classes||=[]) <<c
>  end
> end
> end
>
>
> And I want to ultimately just indescriminately run stuff like this:
>
> class Documents < Sec
> allow Downloads
> end
>
> class Downloads < Sec
> allow Documents
> end
>
> But this is a run-time error unless the classes are prototyped somehow. 
> Like:
>
> class Downloads < Sec; end
>
> class Documents < Sec
> allow Downloads
> end
>
> class Downloads < Sec
> allow Documents
> end
>
> As a framework, this would be so much nicer for the end-user if it
> does that automatically, so she doesnt have to thing about declaration
> order.  So thats the problem.  Possible solutions I've tried:


harp:~ > cat a.rb
class Sec
   ALLOWED_CLASSES = []

   def self.allowed_classes
     ALLOWED_CLASSES
   end

   def self.allow *list
     allowed_classes.push *list
     allowed_classes.uniq!
     allowed_classes
   end

   def self.const_missing c
     c
   end

   def self.allowed
     allowed_classes.map{|c| eval c.to_s }
   end
end

class Documents < Sec
   allow Downloads
end

class Foobar < Sec
   allow Downloads
end

class Downloads < Sec
   allow Documents, Foobar
end

p Sec.allowed



harp:~ > ruby a.rb
[Downloads, Documents, Foobar]


i'd push/pop that 'const_missing' handler during the 'allow' method to avoid
any nasty recursion.  but there ya go.

-a
-- 
suffering increases your inner strength.  also, the wishing for suffering
makes the suffering disappear.
- h.h. the 14th dali lama