From: Todd Benson <caduceass@...>
Date: 2007-07-24T08:25:13+09:00
Subject: Re: Inherited & load

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