vision_request_overview.swift

let requestHandler = VNImageRequestHandler(url: inputImageURL) 
let request = VNDetectRectanglesRequest { request, error in
    self.completedVisionRequest(request, error: error)
}

// perform additional request configuration
request.usesCPUOnly = false //allow Vision to utilize the GPU

DispatchQueue.global().async { 
    do { 
        try requestHandler.perform([request]) 
    } catch { 
        print("Error: Rectangle detection failed - vision request failed.") 
    } 
}