From: Robert Klemme <shortcutter@...>
Date: 2006-12-27T01:35:09+09:00
Subject: Re: YAML problem with serializing of nested object structures

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On 26.12.2006 15:11, Kjetil Orbekk wrote:
> Hi!
> 
> I'm making a graph tool, and i have some problem with the
> serialization of my graphs. The problem comes when i try to load a
> graph i earlier serialized with YAML. In the objects i serialize, I
> have two instance variables (arrays, as below) that contain some other
> objects of similar type (also serialized). I managed to reproduce the
> problem with a simpler object structure below. To me, this seems very
> wierd, especially since it saves some data and breaks it when
> loading. Could it be a bug, or am I doing something wrong here?
> 
> ruby --version is "1.8.4 (2005-12-24) [i486-linux]". My operating
> system is Debian GNU/Linux 4.0.

First of all, there does not seem to be an issue with general recursive 
structures:

$ irb -r yaml
irb(main):001:0> a=[1]
=> [1]
irb(main):002:0> b=[2,a]
=> [2, [1]]
irb(main):003:0> a << b
=> [1, [2, [...]]]
irb(main):004:0> b
=> [2, [1, [...]]]
irb(main):005:0> str = a.to_yaml
=> "--- &id001 \n- 1\n- - 2\n  - *id001\n"
irb(main):007:0> c = YAML.load str
=> [1, [2, [...]]]
irb(main):008:0> c[1]
=> [2, [1, [...]]]

I changed your code a bit (attached) but with no new results.  It seems, 
you actually hit a bug in YAML.  Marshal does not seem to have this 
problem (see last output).  So, if the output needs not be readable then 
this is definitively an alternative - and it's also faster IIRC.

Kind regards

	robert

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require "yaml"
require 'pp'

# Test class with two instance variables to hold arrays with similar
# objects
class Test
  attr_accessor :c1, :c2
  def initialize(c1=[], c2=[]) @c1, @c2 = c1, c2 end
end

a = Test.new
b = Test.new([a],[Test.new])
a.c1 << b
a.c2 << b

# The problem comes when saving the whole thing as an array
ary = [a, b]
puts "Original:"
pp ary
puts ""

yaml1 = YAML.dump(ary)

# +ary_from_yaml[0]+ looses its c2 even though it's clearly in the YAML output
ary_from_yaml = YAML.load(yaml1)
puts "Copy:"
pp ary_from_yaml
puts ""

yaml2 = YAML.dump(ary_from_yaml)

print "YAML 1\n" + yaml1 + "\n\n"
print "YAML 2\n" + yaml2 + "\n\n"

p "YAML1", yaml1
p "YAML2", yaml2

print "YAML 1 length: #{yaml1.length} \tYAML 2 length: #{yaml2.length}\n"

pp Marshal.load(Marshal.dump(ary))


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