Swift 2.0 Error Handling Asynchronous Functions

Swift 2.0 Error Handling Asynchronous Functions

**** Medium Story ****
https://medium.com/ios-os-x-development/logan-wright-i-just-started-dabbling-with-swift-s-error-handling-myself-5e7b3dffdf06#.zbor79r8l

public enum Errors: ErrorType {
    case NoInternetConnection
    case QueryResponseError
    case ErrorQueryingForData
    case QueryDataEmpty
    
    public func message() -> String {
        switch self {
        case .NoInternetConnection:
            return "No internet connection!\nMake sure your device is connected to begin search"
        case .QueryResponseError:
            return  "Query response invalid!"
        case .ErrorQueryingForData:
            return  "Query Error!"
        case .QueryDataEmpty:
            return "QueryData Empty!"
        }
    }
    static let allErrors = [NoInternetConnection, QueryResponseError, ErrorQueryingForData, QueryDataEmpty]
}

public func querySomething(queryString: String, completion: (result: () throws -> NSData) -> Void) -> Void {
    
    if let queryUrl: NSURL = NSURL(string: queryString) {
        
        let session = NSURLSession.sharedSession()
        
        let task = session.dataTaskWithURL(queryUrl, completionHandler: { (queryData, response, error) -> Void in
            
            guard error == nil else { return completion(result: {throw Errors.ErrorQueryingForData})}
            guard queryData != nil else { return completion(result: {throw Errors.QueryDataEmpty})}
            
            return completion(result: { queryData! })
            
        })
        task.resume()
    }
}

querySomething("http://www.google.ca") { (result) -> Void in
    
    do {
        
        let result = try result()
        
        // 1. Parse results
        
        // 2. Load UI on main queue
        dispatch_async(dispatch_get_main_queue(), { () -> Void in
            
        })
        
    } catch {
        
        // handle error
        if let error = error as? Errors {
    
            switch error {
                
            case .ErrorQueryingForData:
                print(error.message())
            case .QueryDataEmpty:
                print(error.message())
            default:
                break
            }
        }
    }
 }