From: Joel VanderWerf <vjoel@...>
Date: 2005-09-26T06:53:58+09:00
Subject: Re: Concerning Marshalling

ts wrote:
>>>>>>"c" == christophe poucet@gmail com <christophe.poucet@gmail.com> writes:
> 
> 
> c> That's why I tried something as follows:
> 
>  Perhaps best to use marshal_dump/marshal_load
> 
> Guy Decoux

That's a good suggestion. The marshal_dump/marshal_load pair can be very
useful, because it integrates well with the whole Marshal.dump or
Marshal.load process. An inherent problem with _dump and _load is that
you have to use strings, so you are responsible for somehow preserving
and restoring references to other objects that are also being dumped.
This is critical when the original dump call was on an object that
referred to your object, not directly to your object.

With marshal_dump/marshal_load, you produce/consume an arbitrary
Marshallable object, possibly containing references, and all the code in
marshal.c takes over the hard task of preserving and restoring
references. Probably an example will say it better:

class Node
  attr_accessor :prev_node, :next_node

  attr_accessor :temp_data
    # don't want this to persist (maybe it's a cache, or simply
    # undumpable, like a proc, or a file, or a singleton).

  def marshal_dump
    dumped_obj = [prev_node, next_node]
    dumped_obj
  end

  def marshal_load(dumped_obj)
    @prev_node, @next_node = dumped_obj
  end
end

node1 = Node.new
node2 = Node.new
node1.next_node = node2
node2.prev_node = node1
node1.temp_data = STDOUT
node2.temp_data = proc {"foo"}

p node1

p Marshal.load(Marshal.dump(node1))

__END__

output:

#<Node:0xb7dff098 @next_node=#<Node:0xb7dfef08
@prev_node=#<Node:0xb7dff098 ...>, @temp_data=#<Proc:0xb7dff37c@-:23>>,
@temp_data=#<IO:0xb7e4c078>>
#<Node:0xb7dfed64 @prev_node=nil, @next_node=#<Node:0xb7dfed28
@prev_node=#<Node:0xb7dfed64 ...>, @next_node=nil>>

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407