class Psych::Visitors::YAMLTree::Registrar

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

def initialize
  @obj_to_id   = {}.compare_by_identity
  @obj_to_node = {}.compare_by_identity
  @counter     = 0
end

def key? target
  @obj_to_node.key? target
end

def node_for target
  @obj_to_node[target]
end

def register target, node
  @obj_to_node[target] = node
end