From: Robert Dober <robert.dober@...>
Date: 2007-07-24T17:38:13+09:00
Subject: Re: Inherited & load

On 7/24/07, Todd Benson <caduceass@gmail.com> wrote:
> On 7/23/07, F. Senault <fred@lacave.net> wrote:
> > Hello.
> >
> > I've written a mechanism to dynamically load plugins inheriting from a
> > base class, using the self.inherited method.
> >
> > Now, in an irb session, I noticed that, even if I (re)load the classes,
> > the self.inherited is only triggered once.  Short example :
> >
> > > ruby -v
> > ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-freebsd6]
> >
> > > cat first.rb
> > #! /usr/local/bin/ruby
> > load "test.rb"
> > load "test.rb"
> >
> > > cat test.rb
> > #! /usr/local/bin/ruby
> > class Test
> >   def self.inherited(c)
> >     puts "#{c} inherited Test !"
> >   end
> > end
> > load "test2.rb"
> >
> > > cat test2.rb
> > #! /usr/local/bin/ruby
> > puts "In #{__FILE__}."
> > class Test2 < Test ; end
> >
> > > ruby first.rb
> > In ./test2.rb.
> > Test2 inherited Test !
> > In ./test2.rb.
> >
> > Is there a trick somewhere that would allow me to trigger the inherited
> > method at each time the file containing the "sub-class" (e.g. Test2) is
> > loaded ?
> >
> > (The real plugin class, if there is a need, is here :
> > http://www.lacave.net/~fred/projets/plugin.rb )
> >
> > Fred
>
> This is probably not much help, but you got me to learn a couple of
> things while playing around.
>
> First of all, I don't think you can inherit more than once without
> removing the constant.  Once you've declared class B < A then that's
> it until removed.  For example,
>
> irb> class A; def self.inherited(s); puts "#{s}!"; end; end
> => nil
> irb> class B < A; end
> B!
> => nil
> irb> class B < A; end
> => nil
> irb> class C;end
> => nil
> irb> class B < C; end
> =>TypeError: superclass mismatch for class B
>   ....blah blah
>
> But, if you use a module,
>
> $ cat m.rb
> module M
>   class A
>     def self.inherited o
>       puts "A inherited by #{o}!"
>     end
>   end
>   def self.delete const
>     remove_const const.intern
>   end
> end
>
> $ cat test.rb
> require "m"
>
> puts "\nConstants: #{M.constants.inspect}"
> print "First inherit: "
> class M::B < M::A; end
>
> puts "\nConstants: #{M.constants.inspect}"
> print "Second try at inherit: "
> class M::B < M::A; end
>
> print "\n\nDelete B"
> M::delete "B"
> puts "\nConstants: #{M.constants.inspect}"
> print "Try inherit now:"
> class M::B < M::A; end
> puts
> $
>
> Todd
>
>
Hmm not sure how this fits in but what about include instead of
inherit, does this not what you want to achieve?
The more I am thinking about it I feel that this might indeed be what
is needed as Module#included is executed all the time the include
statement is called, hopefully Fred can use inclusion instead of
inheritance.

Cheers
Robert


-- 
I always knew that one day Smalltalk would replace Java.
I just didn't know it would be called Ruby
-- Kent Beck