Swift 2: Throw from closure

问题

I'm upgrading my code to Swift 2 using error handling with try-catch. I've stuck with closure (NSURLSession), I can't throw inside it.

Generally I'm using such code:

let request = NSURLRequest()

let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
    data, response, error in
    if error != nil {
        throw(ErrorType) // here some errortype enum
    }
}

But I'm receiving the error: "Cannot invoke dataTaskWithRequest with an argument list of type …". How can I throw from closure?

回答1:

You can't throw inside a closure because the closure can be called later, when the function is already executed.

In your example the closure is called asynchronously after the URLRequest got a response, at this time the calling function is already executed.

来源：https://stackoverflow.com/questions/32668291/swift-2-throw-from-closure