Translation:You will have been able to swim in the pool.
Probably because this form, the future perfect (e.g. 'will have') is rarely used in English language.
In Italian it is often used to provide some uncertainty. To indicate that you are predicting the future, - or asking what it might be. Still in English it can be used in a similar way as part of a sentence like:
I hope you will have been able to swim in the pool before I call you next time.
My text book explains this tense as: "In Italian and English this tense is used to express an action that will happen in the future BEFORE another future action." Because DL so often uses basically incomplete ideas (this one for example) it often does not seem to made sense.
Would have and will have mean completely different things, and both need something adding before they make sense. Would have been able indicates that something that could have happened in the past, for some reason, did not happen. You would normally add a clause starting with if. E.g. if it wasn't so cold. Will have been able carries no conditions. It is going to happen. If you prefix it with something like "by the time I get back from Rome..." it makes perfect sense