Swift Scoping Rules -- nil value after setting a non-nil value - ios

Question

I'm writing a DataService that interfaces with Firebase. I'm setting self.realID within a closure and when I reference it outside the closure, it fails because it unwraps a nil value. Why is this happening?
My file:
import Foundation
import Firebase
class Database {
var firebaseRef = Firebase(url:"https://<<UNIQUE>>.firebaseio.com")
class var sharedInstance: Database {
struct Data {
static var instance: Database?
static var token: dispatch_once_t = 0
}
dispatch_once(&Data.token) {
Data.instance = Database()
}
return Data.instance!
}
var uid : String!
var realID : String!
var validated = false
func validate(user: String, study: String) -> Bool {
firebaseRef.authUser(user+"#example.com", password: user,
withCompletionBlock: { error, authData in
if error != nil {
NSLog(String(error))
} else {
self.uid = authData.uid
NSLog(authData.uid)
}
})
let usersRef = Firebase(url: "https://<<UNIQUE>>.firebaseio.com/users")
usersRef.observeEventType(FEventType.Value, withBlock: { (snapshot) in
let value = snapshot.value.objectForKey("study") as! String
self.realID = value
NSLog(self.realID) // this is a non-nil value
})
NSLog("About to encounter nil value and crash")
if self.realID == study {
return true
}
return false
}
}
How do i prevent this fatal error from happening?

Answer 1

You need to add a completionHandler because it is async request. If you will set the break points then return is executed before you are setting the id.
func validate(user: String, study: String, completionHandler:(Bool) -> Void) {
let usersRef = Firebase(url: "https://<<UNIQUE>>.firebaseio.com/users")
usersRef.observeEventType(FEventType.Value, withBlock: { (snapshot) in
if let value = snapshot.value.objectForKey("study") as? String {
self.realID = value
completionHandler(true)
} else {
completionHandler(false)
}
})
}
UPDATE
validate("Rahul", study: "Study") { (value: Bool) in
if value {
} else {
}
}