In the new romantic comedy “What If,” director Michael Dowse wants to recapture the same kind of screwball, verbal-sparring energy characteristic of classic Cary Grant and Katherine Hepburn comedies such as “Bringing Up Baby” and “His Girl Friday.”

The two young, potential lovers — played by “Harry Potter” superstar Daniel Radcliffe and Zoe Kazan — deliver their lines at rapid-fire speed, as if they’ve just done a few lines of cocaine each. Like with Hepburn and Grant, Radcliffe and Kazan are locked in a contest to see who can dominate the other using verbal wit. As a result, the picture moves at sprint through each scene, making the already-brisk, 90-minute run time feel even more brisk.

Luckily, the movie doesn’t overstay its welcome, but not very much is accomplished by the film’s end, either.

This is primarily because “What If” isn’t nearly as nutty and unpredictable as either “Baby” or “Friday.” Instead, it unfolds like your standard, quirky, 20-something, romantic comedy, with very little surprises.

Radcliffe plays Wallace, a medical-school dropout who — after breaking up with his girlfriend — has become sour and pessimistic toward relationships. Kazan plays Chantry, an intelligent, slightly kooky gal who doesn’t realize her full potential as an animator; at her job, she’s turned down numerous promotions.

One night, at a party, the two hit it off real well, except there’s one problem: She’s got a boyfriend. He’s a U.N. worker named Ben (Rafe Spall), a nice guy who’s also kind of dull. Wallace and Chantry decide to be friends, but for Wallace, that’s not good enough.

According to rom-com rules, our leads must have friends who serve as advisors to the brewing relationship. Wallace has his free-spirit pal, Allan (Adam Driver), and Chantry has her feisty sister Dalia (Megan Park). The two serve their purpose: to crack more jokes and give bad advice. To his credit, Driver owns his role and, oftentimes, steals the scenes he’s in.

Most of the humor is dialogue-driven, but there are a few inspired physical gags. For example, the scene when Wallace accidently pushes Ben out of a two-story window after he tries to mend his eye injury is so random and out-of-left-field that it works extremely well in a screwball comedy sort of way.

Obviously, Radcliffe and Kazan aren’t on the same level as Hepburn and Grant when it comes to banter, but that’s not exactly a fair comparison. Radcliffe continues to shine in his post-Potter acting career, excelling at playing the charming cynic. Meanwhile, Kazan has a loopy intelligence to her that makes her fun to watch. She may be weird and sometimes awkward, but she’s never a ditz or a bimbo. Their chemistry makes the picture continually watchable.

“What If” is a fine romantic comedy, but it doesn’t do much to innovate the genre.