你的问题属于一种语言现象，不是个例。从本质上讲就是：现在完成时，用在“时间状语从句”或者“条件状语从句”中，表示将来业已完成的动作或状态，代替将来完成时。这跟“主将从现”是一个道理。例如：

1. 时间状语从句：until, as soon as, when

Stay in the house until the danger has passed.  躲在家里，直到危险过后再出来。

I'm very busy now; wait until things have eased up a little.  我现在非常忙，等事情缓一缓再说。

Don't drink the water until it has been cooled.  直到水冷了之后再喝。

We can't move in until the electricity has been laid on.  我们得等电源接通后才能搬进去。

I'll go to my granny's as soon as I have finished my homework. 我一完成作业就去奶奶家。

As soon as he has regained his memory, the problem will be solved.  只要他一恢复记忆，问题就可以解决了。

Put the book back when you have done with it. 你读完这本书时把它放回原处。

When you have formed a plan, you must carry it out. 计划订出之后，你必须贯彻执行。

The hen cackles when she has laid an egg. 母鸡下蛋就咯咯地叫。

2. 条件状语从句：if, once, as long as

If you have finished reading the book before I leave, please lend it to me. 如果你在我离开之前就读完了这本书，请借给我。

If he has written the letter, I'll post it. 如果他写完了信，我就把它寄走。

Once we have promised, we should keep it. 一旦许下诺言，我们务必遵守。

We cannot move him from any decision once he has made it. 他一旦做出决定，我们就无法使他改变。

You can watch TV as long as you have finished your homework. 只要完成了作业，你就可以看电视。

As long as you have passed the previous three relevant practice game, we can end the confrontation between rivals. 只要你通过了前面三关的练习赛，就可以对决最终的对手。

3. 偶尔还用在让步状语从句中

Even though you have set the bird free, it can hardly survive.  就算将来你放了这只鸟，它也很难活。

【注意】主句部分是个祈使句，实际上相当于一个一般将来时的句子，因为祈使句的动作都是将来才发生的。此外，以上各个从句中，我们可以用一般现在时代替现在完成时，意思差别不大。