Your friend is right. It can't.

You can for open water swimming but not pool swimming. If you don't care about pace or distance you could use the open water profile

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Personal best:
Ironman 9:22:02
Ironman 70.3 4:20:00

I've enjoyed checking my stroke rate/strokes per length & Swolf during rest intervals any time I create a lap on the v800, however the new look of the lap screen doesn't show this since the recent firmware "update". The data shown for these metrics is screwy when viewing lap data post workout too, saying things like 11584/pool and 11584/min 11584 SWOLF. It gives correct data for these metrics for the entire swim, but this is an average for the entire workout and the statistics from my warmup/cooldown dilute the more pertinent information of my main set which I more interested in knowing. I am hopeful that this new bug is fixed with the next firmware update.

Being able to see the stroke rate after pressing lap would be fine! Unfortunately this is not possible after the update.

By the way, do you press the lap button under water? Polar states that it is 'not recommended' to press buttons under water ;(

how would you be able to see it real time during swimming???

Do not hit the lap button while swimming, I use the tap feature by slapping the watch when I want to start/finish a lap.