Imitating Elixir's Stream.unfold/2 in Ruby

unfold.rb

class Enumerator
  def self.unfold tuple
    new do |yielder|
      loop do
        current, tuple = yield tuple
        yielder << current
      end
    end
  end
end

FiveAndDown = Enumerator.unfold 5 do |n|
  [n, n - 1]
end
FiveAndDown.first 10
#=> [5, 4, 3, 2, 1, 0, -1, -2, -3, -4]

Fibonacci = Enumerator.unfold [0, 1] do |a, b|
  [a, [b, a + b]]
end
Fibonacci.first 10
#=> [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]