你的句子可以分为两类：

▲一类是将来完成时，如你的第一句：

There will have been a definite result before Friday. 星期五以前肯定会有结果。

本句中的 will 不是情态动词，而是助动词，它不是“情态动词+have+done”结构，而是将来完成时，又如：

I expect you will have changed your mind by tomorrow. 我预料到明天你就会改变主意了。

By the end of next week, I will have been a teacher for 25 years. 到下周末，我当老师就有25年了。

As you will have noticed, there are some gaps in the data. 你也许已经注意到了，数据里有些缺漏。

By the time the case comes to trial, he will have spent a year in prison. 到这个案件开庭审理时，他将已经在监狱里呆了一年了。

将来完成时用于表示到将来某一时刻已经完成的动作。例如下面这句：

I will have retired by the year 2020. 到2020年我将已退休。（意思是：在2020年或这之前，我退休已成为过去的事)

▲另一类就是你说的“情态动词+have+done”结构——这类结构与将来完成时的用法相似，但根据所用的情态动词不同，与将来完成时相比，增添了一定的“情态”意义（比如推测）。例句如：

I should have finished reading it by Friday. 我大概到星期五能把它看完。（牛津高阶词典）

She said she might have finished by this afternoon but don’t hold your breath. 她说她有可能在今天下午之前完成，不过你可别眼巴巴等着。（剑桥高级英语词典）

We should have finished by a quarter past two and the bus doesn't leave till half past. 我们2:15之前应该会完成，汽车要到2:30才开。（柯林斯高级英语词典）

关于此类用法，《牛津英语用法指南》作出的相关解释是：

may / might+动词不定式完成式也可以表示现在或将来 (如同现在完成时和将来完成时)。如：

I’ll try phoning him, but he may have gone out by now. 我要给他打电话，但他现在可能出去了。

By the end of this year I might have saved some money. 到今年年底，我就可能积攒了一点儿钱了。