From: Danny Sofer <danny@...>
Date: 2001-02-06T01:40:02+09:00
Subject: [ruby-talk:10375] Problems creating persistent objects

Here's the synopsis:

module Storage
  def store
    puts "should be storing #{@f}"
    File.open(@f, "w") { |f| Marshal.dump(@data, f) }
  end
  def retrieve
    File.open(@f) { |f| return Marshal.load(f) }
  end
end

class Obj
  include Storage
  def initialize(f, m='')
    @f = f
    puts "the file is #{@f}"
    @data = {}
    @data['m'] = ''
    if File.exists?(@f)
      @data = retrieve
    end
    puts "Old value : #{@data['m']}"
    @data['m'] = m
    puts "New value : #{@data['m']}"
    ObjectSpace.define_finalizer(self, proc { store } )
   end
end

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


I am attempting to create persistent objects, which automatically load
themselves (if there's a previously stored version) on creation and store
themselves before they die.

Two problems:

1) i wanted to do something like: "self = retrieve", but in the end settled
for putting my data in to a hash (@data) and storing that instead, because
assigning anything to self is a bit naughty. is there a more elegant way to
round this?

2) by the time the finalizer is called, all my instance variables seem to
have disappeared, so i can't automatically store my data. any other
suggestions?

Finally, I am new to ruby and have just been blown away by it. i can't
remember the last time i was so excited about programming.

many thanks,

danny.