enumerator_fiber.rb

Thread.current[:fiber_local] = :ok

def enumerator
  Enumerator.new do |yielder|
    yielder.yield Thread.current[:fiber_local]
  end
end

p enumerator.next  # => nil
# which is explained by, can be reduced to:
p Fiber.new { Thread.current[:fiber_local] }.resume # => nil

p enumerator.to_a  # => [:ok]
p enumerator.first # => :ok
enumerator.each do |value|
  p value # => :ok
end