prime.rb

pseudo_prime_generator.rb

  class PseudoPrimeGenerator
    include Enumerable

    def initialize(ubound = nil)
      @ubound = ubound
    end

    def upper_bound=(ubound)
      @ubound = ubound
    end
    def upper_bound
      @ubound
    end

    # returns the next pseudo-prime number, and move the internal
    # position forward.
    #
    # +PseudoPrimeGenerator+#succ raises +NotImplementedError+.
    def succ
      raise NotImplementedError, "need to define `succ'"
    end

    # alias of +succ+.
    def next
      raise NotImplementedError, "need to define `next'"
    end

    # Rewinds the internal position for enumeration.
    #
    # See +Enumerator+#rewind.
    def rewind
      raise NotImplementedError, "need to define `rewind'"
    end

    # Iterates the given block for each prime numbers.
    def each(&block)
      return self.dup unless block
      if @ubound
        last_value = nil
        loop do
          prime = succ
          break last_value if prime > @ubound
          last_value = block.call(prime)
        end
      else
        loop do
          block.call(succ)
        end
      end
    end

    # see +Enumerator+#with_index.
    alias with_index each_with_index

    # see +Enumerator+#with_object.
    def with_object(obj)
      return enum_for(:with_object) unless block_given?
      each do |prime|
        yield prime, obj
      end
    end
  end