Reverse geocoding in Swift 4

Question

I'm attempting to write a simple method that's fed CLLocationDegrees and returns a CLPlacemark. Looking at Apple's documentation, it seems like a simple task.

Below is what I've dumped into a playground:

import CoreLocation
// this is necessary for async code in a playground
import PlaygroundSupport 
// this is necessary for async code in a playground
PlaygroundPage.current.needsIndefiniteExecution = true

func geocode(latitude: CLLocationDegrees, longitude: CLLocationDegrees) -> CLPlacemark? {
    let location = CLLocation(latitude: latitude, longitude: longitude)
    let geocoder = CLGeocoder()
    var placemark: CLPlacemark?
    geocoder.reverseGeocodeLocation(location) { (placemarks, error) in
        if error != nil {
            print("something went horribly wrong")
        }
        if let placemarks = placemarks {
            placemark = placemarks.first
        }
    }
    return placemark
}
let myPlacemark = geocode(latitude: 37.3318, longitude: 122.0312)

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As it stands, my method is returning nil. I'm not sure where my error lies, but I rest assured it's something starlingly stupid on my part. Thank you for reading.