# File lib/backports/1.8.7/enumerable.rb, line 183
  def one?
    found_one = false
    if block_given?
      each do |o|
        if yield(o)
          return false if found_one
          found_one = true
        end
      end
    else
      each do |o|
        if o
          return false if found_one
          found_one = true
        end
      end
    end
    found_one
  end