aka Future Perfect Continuous
English's future perfect progressive expresses an action that will have been happening at a particular time in the future, with an emphasis on the course or duration of the action taking place in the past. It indicates "the ongoing past in the future"; that is, it refers to something that is ongoing in the past from the viewpoint of the future.
The future perfect progressive is formed as follows:
will + have + been + verb with -ing
- By then, he will have been talking for an hour.
(Talking now, looking back from a time in the future to his ongoing talking.)
- I will have been studying French for ten years by next July.
(Talking now, looking back from next July to my ongoing studies.)
Note: The future perfect progressive is not used very often in everyday English as it can usually be replaced by the future perfect.