Single unwrap inside block in Swift

Question

This gives me an error:

NSNotificationCenter.defaultCenter().addObserverForName(MyNotification, object: nil, queue: nil) { (notification: NSNotification?) in
    self.variable?.myMethod()
}

But this is fine:

NSNotificationCenter.defaultCenter().addObserverForName(MyNotification, object: nil, queue: nil) { (notification: NSNotification?) in
    println()
    self.variable?.myMethod()
}

Any idea why and how to solve it?

Thank you.

Answer 1

What you're seeing is "implicit returns". Swift assumes that if you have a single expression as the implementation of a closure, then it returns the result of that line of code from the closure. This is a optimization documented in Apple's Swift Programming Language text (check the last paragraph/bullet list in the Closures intro).

Because of this, if you're required to have a return statement if you don't want to implicitly return from the first statement.

So your code should look like:

NSNotificationCenter.defaultCenter().addObserverForName(MyNotification, object: nil, queue: nil) { (notification: NSNotification?) in
  self.variable?.myMethod()
  return
}