future.rb

future.rb

class Future
  def initialize(&block)
    @que = Queue.new
    @t = Thread.new {
      @que << block.call
    }
  end
  def value
    return @que.pop
  ensure
    @que.close
    @t.join
  end
end

future = Future.new do
  sleep 3.0
  'done'
end
p 'ok'
sleep 2.0
p future.value