class Density
  include Enumerable
  extend Forwardable

  attr_accessor :uniform, :fail, :exact, :d
  def_delegators :@d, :each, :[], :[]=, :inspect, :delete

  def initialize(num=0)
    @d=Hash.new(Rational(0))
    @d[num]=Rational(1)
    @uniform=true
    @exact=true
    @fail=false
  end

  ... (many things, e.g. +() operator
end