quick_emit.rb

require "yaml"

class A
  def initialize
    @b = B.new
  end
end

class B
  def to_yaml emitter
    puts emitter.class # YAML::Syck::Emitter
    puts emitter.class.ancestors.inspect # [YAML::Syck::Emitter, Object, Kernel]
    puts (emitter.methods - Object.new.methods).sort.inspect # ["emit", "level", "level=", "node_export", "reset", "set_resolver"]

    YAML.quick_emit(object_id, emitter) do |out|
      puts out.class # YAML::Syck::Out
      puts out.class.ancestors.inspect # [YAML::Syck::Out, Object, Kernel]
      puts (out.methods - Object.new.methods).sort.inspect # ["emitter", "emitter=", "map", "scalar", "seq"]

      out.map("tag:ruby.yaml.org,2002:object:B", to_yaml_style) do |map|
        puts map.class # YAML::Syck::Map
        puts map.class.ancestors.inspect # [YAML::Syck::Map, YAML::Syck::Node, YAML::BaseNode, Object, Kernel]
        puts (map.methods - Object.new.methods).sort.inspect # ...
      
        map.add("b_attr", "some value")
      end
    end
  end
end

a = A.new
a.to_yaml