What If Daniel Radcliffe, Zoe Kazan, Adam Driver. Directed by Michael Dowse. Rated PG-13. Opens Friday.

Cast Daniel Radcliffe as the male lead in a romantic comedy that asks whether men and women can be platonic friends, and people will inevitably dub the result When Harry Potter Met Sally. Consequently, the director of What If, Michael Dowse (Goon), doesn’t shy away from the comparison, having his characters attend a screening of Rob Reiner’s previous film, The Princess Bride, and giving the female lead, a young woman named Chantry (Zoe Kazan), Sally’s habit of peeking into the mailbox after depositing a letter, just to make sure it really dropped all the way down. Here, there’s a more practical impediment to the friends becoming lovers: Chantry already has a boyfriend (Rafe Spall), who’s jealous enough to make veiled threats while holding large kitchen knives. Same basic idea, though: They meet cute, they stall, they clinch.

What primarily matters in a film like this is the charm of the performances and the wittiness of the banter. What If holds its own in both departments, though Radcliffe and Kazan are perpetually in danger of being upstaged by Adam Driver (Girls) and Mackenzie Davis (Halt and Catch Fire), playing the requisite subsidiary couple. For a while, it even looks as if our heroes might actually remain just friends, which would still qualify as genuinely revolutionary a quarter-century after Harry finally kissed Sally. That’s far too risky for a movie this derivative, though, and an improbably convenient happy ending is duly manufactured. The real question is: What if someone made a rom-com that didn’t strictly adhere to formula?