Rails::Initializable::Collectionのtsort_eachはこんな感じ

tsort_example.rb

class Node
  attr_reader :before, :after, :name
  def initialize(name, config)
    @name = name
    @before = config[:before]
    @before = config[:after]
  end
  def to_s
    @name
  end
end
require 'tsort'
class TSortArray < Array
  include TSort
  alias tsort_each_node each
  def tsort_each_child(node, &block)
    select {|i| i.before == node.name || i.name == node.before} 
  end
  def add(*args)
    config = args.last.kind_of?(Hash)? args.pop: {}
    self << Node.new(args.first, config)
  end
end
a = TSortArray.new 
a.add :t7 
a.add :t5, :after => :t11
a.add :t3, :after => :t8
a.add :t11, :before => :t7, :after => :t2
a.add :t8, :before => :t7
a.add :t2
a.add :t9
a.add :t10
result = []
a.tsort_each {|i| result << i }
puts result.inspect #=> [t7, t5, t3, t11, t8, t2, t9, t10]

wikipediaのトポロジカルソートの例と同じDAGになります。