From: Aleks Kissinger <aleks0@...>
Date: 2006-07-26T22:30:11+09:00
Subject: Re: Automagic class prototyping

I can see some pitfalls here, but this is the most promising technique
I've seen so far.

On 7/26/06, ara.t.howard@noaa.gov <ara.t.howard@noaa.gov> wrote:
> 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
>
>