Getting extensions of a given UTType

Swift 5

import MobileCoreServices

static func fileExtension(for dataUTI: String) -> String? {
    guard let fileExtension = UTTypeCopyPreferredTagWithClass(dataUTI as CFString, kUTTagClassFilenameExtension) else {
        return nil
    }

    return String(fileExtension.takeRetainedValue())
}

UTTypeCopyPreferredTagWithClass is used to convert a UTI to another tag, like file extensions:

NSString *extension = (__bridge_transfer NSString *)UTTypeCopyPreferredTagWithClass(myUTI, kUTTagClassFilenameExtension);