Enumerable_xor.rb

module Enumerable
  # requires `other` to respond to .each
  def ^(other)
    result = {}
    seen   = {}
    each do |v|
      result[v] = true
    end
    other.each do |v|
      next if seen.key?(v)
      seen[v] = true
      if result.key?(v)
        result.delete(v)
      else
        result[v] = true
      end
    end

    result.keys
  end
end