From: Brian Marick <marick@...>
Date: 2008-08-20T08:45:17+09:00
Subject: YAML dumping custom object that needs type conversions

I want to use Ruby 1.8.6 YAML to dump this (simplified) object:

    class T < Struct.new(:template)

The :template accessor stores a class, which isn't something that YAML  
can dump. So it seems I need to convert it to a string going out:

    def to_yaml(io)
	.... template.name ....

... and then back into a class when it's read back in:

    YAML.add_domain_type('exampler.com,2008', 'T') { | type, val |
         T.new(eval(...something...))
     }

I've been using the last solution for <http://rubyquiz.com/ 
quiz38.html> as a guide, but it turns out that doesn't work. If you  
dump an object of its SProc class, you get this result: "---  
\nproc_src: 1+1\n". And when you read it back in, you get a hash:  
{"proc_src"=>"1+1"}

Here's the code I'd like to see work. Any help appreciated.

require 'yaml'

class T < Struct.new(:template)
   def to_yaml(io)
     YAML::quick_emit(self.object_id, io) { |out|
       out.map("!exampler.com,2008/T" ) { |map|
         map.add("template", template.name)
       }
     }
   end
end

YAML.add_domain_type('exampler.com,2008', 'T') { | type, val |
   T.new(eval("#something#"))
}


d = YAML.dump([T.new(Object)])
puts d.inspect
puts YAML.load(d).inspect




-----
Brian Marick, independent consultant
Mostly on agile methods with a testing slant
www.exampler.com, www.exampler.com/blog, www.twitter.com/marick