From: Danny Sofer <danny@...>
Date: 2001-02-07T01:40:02+09:00
Subject: [ruby-talk:10430] Re: Problems creating persistent objects

"Danny Sofer" <danny@sofer.com> wrote

> Here's the synopsis:
>

<snip>

Thanks for the responses. they were very helpful. there follows an amended
code snippet.

'Storage' can be used with any class that includes and extends it. the only
requirement is that there be a publically readable instance variable called
f, that is the first argument of any call to 'new'.

ObjectSpace.each_object is used to pick up the object and save it before it
gets destroyed. this seems a bit of a kludge, but it's the only way i could
work out to reference the object. is there a better way?

module Storage
  def new(f, *args)
    ObjectSpace.define_finalizer(self, proc {finalizer(f)} )
    if File.exists?(f)
      File.open(f) {|fl| return Marshal.load(fl) }
    else
      super
    end
  end
  def finalizer(f)
    ObjectSpace.each_object(Storage) do |s|
      puts s.inspect
      if s.f == f then File.open(f, "w") {|fl| Marshal.dump(s, fl)} end
    end
  end
end

class Obj
  include Storage    # mix in Storage
  extend Storage     # make class methods (i.e. new) available
  attr_reader :f
  def initialize(f, m='')
    @f = f
    @m = m
  end
end

o = Obj.new('.test', 'hello' )

thanks again for your time and bandwidth.

danny