Cannot convert value of type 'inout NSError?'

Question

The errors i'm getting :

1)Extra argument 'error' in call

2) Cannot convert value of type 'inout NSError?' (aka 'inout Optional') to expected argument type '()'

My Code:

func initUdpSocket(){
        var error : NSError?
        mUdpSocket = GCDAsyncUdpSocket(delegate: self, delegateQueue: dispatch_get_main_queue())
        mUdpSocket.enableBroadcast(true,error: &error)
        mUdpSocket.beginReceiving(&error)

    }

    func udpSocket(sock: GCDAsyncUdpSocket!, didReceiveData data: NSData!, fromAddress address: NSData!, withFilterContext filterContext: AnyObject!) {
        print("\(__FUNCTION__),\(__LINE__),\(data)");
    }

    func udpSocket(sock: GCDAsyncUdpSocket!, didSendDataWithTag tag: Int) {
        print("\(__FUNCTION__),\(__LINE__),\(tag)");
    }

    func udpSocket(sock: GCDAsyncUdpSocket!, didConnectToAddress address: NSData!) {
        print("\(__FUNCTION__),\(__LINE__),\(address)");
    }
    func udpSocket(sock: GCDAsyncUdpSocket!, didNotConnect error: NSError!) {
        print("\(__FUNCTION__),\(__LINE__),\(error)");
    }

}

Can i know what is wrong with my codes?? I haven had any errors before updating my xcode.

Swift 2 – I guess you're talking about Swift 2 – introduces a new error handling syntax. It's described in the language guide — vadian

Beltalowda Beltalowda · Accepted Answer · 2016-03-30T04:36:37

Swift 2.2 and Objective-C Interoperability in Error Handling

This appears to be happening because, in Swift 2.2, Objective-C methods that take a NSError ** for their last parameter are converted to the Swift throws method equivalent.

You can find more information on this topic on this page, using the 3rd and 4th sections, excerpted below.

Error Handling (excerpt)

In Cocoa, methods that produce errors take an NSError pointer parameter as their last parameter, which populates its argument with an NSError object if an error occurs. Swift automatically translates Objective-C methods that produce errors into methods that throw an error according to Swift’s native error handling functionality.

For example, consider the following Objective-C method from NSFileManager:

- (BOOL)removeItemAtURL:(NSURL *)URL
                  error:(NSError **)error;

In Swift, it’s imported like this:

func removeItemAtURL(URL: NSURL) throws

Catching and Handling an Error (excerpt)

In Objective-C, error handling is opt-in, meaning that errors produced by calling a method are ignored unless an error pointer is provided. In Swift, calling a method that throws requires explicit error handling.

Here’s an example of how to handle an error when calling a method in Objective-C:

NSFileManager *fileManager = [NSFileManager defaultManager];
NSURL *fromURL = [NSURL fileURLWithPath:@"/path/to/old"];
NSURL *toURL = [NSURL fileURLWithPath:@"/path/to/new"];
NSError *error = nil;
BOOL success = [fileManager moveItemAtURL:URL toURL:toURL error:&error];
if (!success) {
    NSLog(@"Error: %@", error.domain);
}

And here’s the equivalent code in Swift:

let fileManager = NSFileManager.defaultManager()
let fromURL = NSURL(fileURLWithPath: "/path/to/old")
let toURL = NSURL(fileURLWithPath: "/path/to/new")
do {
    try fileManager.moveItemAtURL(fromURL, toURL: toURL)
} catch let error as NSError {
    print("Error: \(error.domain)")
}

Additionally, you can use catch clauses to match on particular error codes as a convenient way to differentiate possible failure conditions:

do {
    try fileManager.moveItemAtURL(fromURL, toURL: toURL)
} catch NSCocoaError.FileNoSuchFileError {
    print("Error: no such file exists")
} catch NSCocoaError.FileReadUnsupportedSchemeError {
    print("Error: unsupported scheme (should be 'file://')")
}

Question-specific Code

In this code example, this means that, in Swift 2.2, the enableBroadcast(error:) method of GCDAsyncUdpSocket would be enableBroadcast() throws and would need to use an explicit do-catch.

Similarly, the beginReceiving() method of GCDAsyncUdpSocket would turn into beginReceiving() throws and would also require the use of a do-catch.

Cannot convert value of type 'inout NSError?'

1 Answers