Lineage: Tap into the latent enumerable powers of your class's directed graph!

lineage.rb

require 'set'

def Lineage(enum_name = :lineage, parent_accessor = :parent)
  Module.new do
    define_method enum_name do |&block|
      if block.nil?
        enum_for(enum_name)
      else
        next_parent, visited = self, Set[self]
        while next_parent = next_parent.send(parent_accessor)
          if visited.include? next_parent
            raise "Cycle detected!"
          end
          block.yield next_parent
          visited << next_parent
        end
      end
    end
  end
end

module Lineage
  include Lineage()
end

person.rb

# A simple example

class Person < Struct.new(:name, :parent)
  include Lineage
end

youngest = Person.new("Adam", nil)
(1..10).each do |n|
  youngest = Person.new(n.to_s, youngest)
end

youngest.name #=> "10"
youngest.lineage.map(&:name) #=> ["9", "8", "7", "6", "5", "4", "3", "2", "1", "Adam"]

The #lineage method this mixin provides yields or returns an Enumerator, which lets you do all the cool enumeration stuff like map, reduce, select, each, to_a, etc..