过去将来完成时是什么?用法呢?

过去将来完成时
should / would have done sth.
用法
1、 过去将来完成时表示在过去将来某一时间以前发生的动作,并往往会对过去将来某一时间产生影响.
We hoped that she would have got the plan ready before we came back.我们希望她能在我们回来
之前把计划做好.
He said he would let me have the book as soon as he had read it.他说书一看完就借给我.
2、 过去将来完成时还常用在虚拟语气中,表示与过去的事实相反.如：
If I had seen him this anteroom,I would have told him about it.今天下午我要是见到他,我会
告诉他那件事的.