Quand tu arriveras, j'aurai déjà mangé.
English: When you arrive, I will have already eaten.
The futur antérieur in French is a verb tense used to talk about an action that will have been completed before another action or moment in the future.
Use the futur antérieur to describe an action that will be finished before a specific time or another action in the future. It is often used with time expressions like 'quand', 'lorsque', or 'dès que'.
Quand tu arriveras, j'aurai déjà mangé.
English: When you arrive, I will have already eaten.
Nous serons partis avant midi.
English: We will have left before noon.
Elle aura terminé ses devoirs quand ses amis viendront.
English: She will have finished her homework when her friends come.
Dès que tu auras compris, tu pourras commencer.
English: As soon as you have understood, you can start.