Future perfect for actions completed before a point in the future

The future perfect tense is used to express that an action will be completed before a point in time in the future (any time up to that point). This point can be implied or expressed with a time expression or a clause with a verb in the present simple tense:

It's no use calling him at work; he'll have left.
By next week, they'll have finished painting the rooms.
By the time we get home, the film will have started.