vn_request_completion_example.swift

func completedVisionRequest(_ request: VNRequest?, error: Error?) {
    // Only proceed if a rectangular image was detected.
    guard let rectangles = request?.results as? [VNRectangleObservation] else {
    guard let error = error else { return }
    print("Error: Rectangle detection failed - Vision request returned an error. \(error.localizedDescription)")
    return
    }
    // do stuff with your rectangles
    for rectangle in rectangles {
        print(rectangle.boundingBox)
    }