alter_defer.rb

class Object
  def defer(method, *args)
    @current_fibers ||= []
    @tracepoint ||= TracePoint.trace(:return) do |tp|
      @current_fibers.reverse_each do |fib|
        fib.resume
      end
    end

    @current_fibers << Fiber.new do
      Fiber.yield
      send(method, *args)
    end
  end
end

def hoge
  f = File.new("defer_test.txt", "w")
  f.defer(:close)

  f.write("hogehoge")
end

hoge