Be to + infinitive, future perfect and future perfect continuous

Be to + infinitive

Be to + infinitive is used to talk about formal or official arrangements, formal instructions, and to give orders. It is particularly common in news reports to talk about future events.

We only use be to + infinitive to talk about things that can be controlled by people:
• We don't know where the meteorite is going to land, (not ...the meteorite is to land.)
• I suppose we will all die eventually, (not ...we are all to die...)
We often use be to + infinitive in wh-clauses to say that something must take place first (in the main clause) before something else can take place (in the wh-clause):
• humans are to survive as a species, we must address environmental issues now.
• The law needs to be revised //justice is to be done, (passive form)
Compare the use of be to + infinitive and the present simple for the future in wh-clauses:
• Jones needs to improve his technique //he is to win gold at the next Olympics, and
• Jones has said that he will retire from athletics //he wins gold at the next Olympics.

Future perfect

We use the future perfect to say that something will be ended, completed, or achieved by a particular point in the future
• Let's hope the volcanic eruption will have finished before we arrive on the island.
• Although people are now angry about what he did, I'm sure that his behaviour will soon have been forgotten. (= passive form)
• By the time you get home I will have cleaned the house from top to bottom.
Notice that we can use other modal verbs instead of will to talk about the future in a less certain way:
• By the time you get home I will/may/should have cleaned the house...

Future perfect continuous

 We can use the future perfect continuous to emphasise how long something has been going on by a particular point in the future:
• On Saturday, we will have been living in this house for a year.
• Next year I will have been working in the company for 30 years.
In sentences with the future perfect continuous we usually mention both the particular point in the future ('On Saturday...', 'Next year...') and the period of time until this point ('...for a year', '...for 20 years'). Notice that we don't usually use the future perfect continuous with verbs describing states
• Next month I will have known Derek for 20 years, (not ...will have been knowing...)