Why are the results different? Calling this function via a variable produces the predicted output, calling the function directly returns the closure. It is not life-threatening, but maybe it helps me to understand the basic concepts better.

func swingBat() -> () -> Void {
    var swingCount = 0
    return {
        if swingCount >= 3 {
            print("You're out!")
        } else {
            print("Strike \(swingCount + 1)")
        }
        swingCount += 1
    }
}
let swing = swingBat()
swing()
swing()
swing()
swing()
swingBat()
swingBat()
swingBat()
swingBat()

Maybe I figured it out myself.

swing is just a variable that holds a function

swing() calls than actually the assigned function and let it do its processing.

similar:

swingBat() is the function itself (swingBat().self)

to let actually do the functions its work I have to call it like this: swingBat()() – allthough it's a bit strange looking for me it does the job

Maybe this is an explanation that makes some sense.

Any ideas?

Thank you.

Now I see more clearly. Thank you @roosterboy.