Syntax trouble to use countObjects (synchronous) from Parse

Question

Below is my function in which I have highlighted the code that works (i.e. asynchronous), but what I want is the synchronous code with PFQuery.countObjects(error: NSErrorPointer) to work.

//Count how many violations User has.
func checkViolationStatus(usr: PFUser) -> Int32 {
    var violations: Int32 = 0
    var query = PFQuery(className: PF_BLOCKEDUSERS_CLASS_NAME)
    query.includeKey(PF_BLOCKEDUSERS_USER)
    query.whereKey(PF_BLOCKEDUSERS_USER, equalTo: usr)

    //THIS WORKS BUT IS ASYNCHRONOUS AND I WANT IT TO BE SYNCHRONOUS
    //        query.countObjectsInBackgroundWithBlock {
    //            (count: Int32, error: NSError?) -> Void in
    //            if error == nil {
    //                print("Sean has played \(count) games")
    //                violations = count
    //            }
    //        }

    //WANT TO MAKE IT SYNCHRONOUS -- THIS DOES NOT WORK
    violations = query.countObjects(<#T##error: NSErrorPointer##NSErrorPointer#>)

    return violations

}

How to use query.countObjects(...) correctly here?

Answer 1

Here is the syntax for passing an NSError in countObjects along with code for printing the error should you receive one:

var error: NSError?
violations = query.countObjects(&error)

if error != nil {
    print(error?.localizedDescription)
}

Here is a little explanation to help you further understand that error type.

The NSErrorPointer type is essentially the same as NSError** in Objective-C and indicates that the address of an object, where it actually lives and not just the object’s pointer, is needed to fulfill the argument type. This is a common error-handling pattern in Objective-C.

The & operator allows you to pass such an address to a function. The argument that is passed in can than be modified instead of being limited to only the scope of the function. This is known as an in-out parameter in Swift terminology because what goes in also goes out.