class Psych::Visitors::YAMLTree::Registrar

def id_for target
  @obj_to_id[target.object_id] ||= (@counter += 1)
end

def initialize
  @obj_to_id   = {}
  @obj_to_node = {}
  @targets     = []
  @counter     = 0
end

def key? target
  @obj_to_node.key? target.object_id
rescue NoMethodError
  false
end

def node_for target
  @obj_to_node[target.object_id]
end

def register target, node
  @targets << target
  @obj_to_node[target.object_id] = node
end