Get result of Webservice Call as Block Callback with NSURLSession in Swift2 - ios

Question

I want to get the result of a webservice call as a block callback so I have added the method fetchOpportunities below to my Opportunity model class now I want to call this method from my UIViewController like that:
class HomeViewController: UITableViewController {
override func viewDidLoad() {
super.viewDidLoad()
Opportunity.fetchOpportunities(
success (data) {
}
)
}
}
I guess blocks is not present in Swift but how to replicate a similar behavior ? The call is asynchronous but I need to get the data when the call is completed in my TableViewController to update the TableViewand it can't work with my actual implementation in Objective-C I used to use blocks but what to do with Swift2
Here is the implementation of fetchOpportunities
class func fetchOpportunities() {
let urlPath = "http://www.MY_API_HERE.com"
guard let endpoint = NSURL(string: urlPath) else { print("Error creating endpoint");return }
let request = NSMutableURLRequest(URL:endpoint)
NSURLSession.sharedSession().dataTaskWithRequest(request) { (data, response, error) -> Void in
do {
guard let dat = data else { throw JSONError.NoData }
guard let json = try NSJSONSerialization.JSONObjectWithData(dat, options: []) as? NSDictionary else { throw JSONError.ConversionFailed }
var ops = [Opportunity]()
if let dataArray = json["data"] as? [[String:AnyObject]] {
for op in dataArray {
ops.append( Opportunity(op) )
}
}
print(ops)
} catch let error as JSONError {
print(error.rawValue)
} catch {
print(error)
}
}.resume()
}

Answer 1

Just use closure. The method declaration will be:
class func fetchOpportunities(callback: ([Opportunity]) -> ()) {
// Do all the work here and then send the data like :
callback(ops)
}
In UIViewController:
Opportunity.fetchOpportunities { (data) -> () in
print(data)
}
Efficient JSON in Swift with Functional Concepts and Generics
Learn NSURLSession using Swift Part 1