Swift QR code decoder

qr.swift

import Foundation
import CoreImage

let arguments = CommandLine.arguments
if arguments.count < 2 {
    fatalError("Usage: \(arguments[0]) filename [filename...]")
}
let context = CIContext()
guard let detector = CIDetector(ofType: CIDetectorTypeQRCode, context: context) else {
    fatalError("Unable to initialize detector")
}
for filePath in arguments.dropFirst() {
    let imageURL = URL(filePath: filePath)
    guard let image = CIImage(contentsOf: imageURL) else {
        fatalError("Unable to load image \(filePath)")
    }
    let features = detector.features(in: image)
    print(filePath)
    if features.count == 0 {
        print("No QR codes detected")
        continue
    }
    for feature in features {
        let feature = feature as! CIQRCodeFeature
        let descriptor = feature.symbolDescriptor!
        let payload = descriptor.errorCorrectedPayload
        if let message = feature.messageString {
            print("Payload: \(message)")
        } else {
            print("Payload can't be interpreted as string")
        }
        print(payload.map { String(format: "%02hhx", $0) }.joined())
    }
}