import Vision

// properties on ViewController
var request: VNDetectTextRectanglesRequest?

override func viewDidLoad() {
    super.viewDidLoad()
	let request = VNDetectTextRectanglesRequest(completionHandler: self.visionRequestDidComplete)
    request.reportCharacterBoxes = true
    self.request = request
}
func visionRequestDidComplete(request: VNRequest, error: Error?) { 
    /* ------------------------------------------------------ */
    /* something postprocessing what you want after inference */
    /* ------------------------------------------------------ */
}

// on the inference point
let handler = VNImageRequestHandler(cvPixelBuffer: pixelBuffer)
if let request = request {
	try? handler.perform([self.request])
}