Swift dispatch_after throwing is not a prefix unary operator error

Question

i have the following code:

import SpriteKit
import Foundation

class GameScene: SKScene {
    var occupiedCoordinates: NSMutableArray = NSMutableArray()

    func addShape () {

        //...

        shape.position = CGPoint(x:actualX, y:actualY)
        self.occupiedCoordinates.addObject(NSValue(CGPoint:shape.position))
        let halfDuration = random(min: CGFloat(0.5), max: CGFloat(5))

        //...

        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2*halfDuration), dispatch_get_main_queue(), ^{
            self.occupiedCoordinates.removeObjectAtIndex(0)
            });
    }

}

i used the original snipped GCD: Dispatch After and i get the following message in the line of dispatch_after()

'^' is not a prefix unary operator

any ideas what the problem is?

Answer 1

This is the correct way to pass a closure (i.e. an objective-c block) to a function in swift:

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2 * halfDuration), dispatch_get_main_queue(), { () -> () in
    self.occupiedCoordinates.removeObjectAtIndex(0)
})

or you can also use this compact form:

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2 * halfDuration), dispatch_get_main_queue()) {
    self.occupiedCoordinates.removeObjectAtIndex(0)
}

Suggested reading: Closures