From: Steve Tuckner <STUCKNER@...>
Date: 2003-11-25T01:40:32+09:00
Subject: YAML self reference issue

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I wonder if anyone has an explanation for the behavior of my yamltest.rb
below. When I run it the first time, I get the output:
 
Creating new file
y = A
y2 = A
 
And when I run it a second time I get the following output:
 
y = Hash
y2 = Hash
 
The problem seems to be that if there is a circular loop in a set of
objects, then it loads the object as a Hash and not as a typed object.
If you comment out the line:
 
  @a.x = @a

Then it works fine both times you run it.
 
Any ideas why that is?
 
This is the Prag Programmers distribution
 
ruby -v
ruby 1.8.0 (2003-08-04) [i386-mswin32]
 
Steve Tuckner
 
# -------- yamltest.rb -------------------------
 
require "yaml"
 
class A
 attr_accessor :x
 def initialize(x)
  @x = x
 end
end
 
class YamlTest
 class << self
  def load
   begin
    File.open("test.yaml") do |f|
     YAML::load(f)
    end
   rescue Errno::ENOENT
    puts "Creating new file"
    YamlTest.new
   end
  end
 end
 
 attr_reader :a
 
 def initialize
  @a = A.new(nil)
  @a.x = @a
 end
 
 def save
  File.open("test.yaml", "w") {|f| f.write(self.to_yaml)}
 end
end
 
y = YamlTest.load
puts "y = #{y.a.class}"
y.save
y2 = YamlTest.load
puts "y2 = #{y.a.class}"


Steve Tuckner 


 

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