infinite_enumerators.rb

class InfiniteCycleEnumerator
  def self.enum(num)
    Enumerator.new do |y|
      idx = 0
      loop do
        y << idx % num
        idx = idx + 1
      end
    end
  end
end

class InfiniteArrayEnumerator
  def self.enum(array)
    Enumerator.new do |y|
      cycle = InfiniteCycleEnumerator.enum(array.length)
      loop do
        y << array[cycle.next]
      end
    end
  end
end

# examples

enumerator = InfiniteArrayEnumerator.enum(['one', 'two', 'free'])
# => #<Enumerator: #<Enumerator::Generator:0x0000000c723790>:each>

enumerator.next
# => "one" 
enumerator.next
# => "two" 
enumerator.next
# => "free" 
enumerator.next
# => "one" 
enumerator.next
# => "two" 
enumerator.next
# => "free" 
enumerator.next
# => "one"