Hacky private fields

private

class Counter {
    let inc : () -> Int
    let dec : () -> Int
    init(inc : () -> Int, dec : () -> Int) {
        self.inc = inc;
        self.dec = dec;
    }
}
 
func CounterCreator(initial :Int) -> Counter {
    var storage = initial
 
    return Counter(inc: {return ++storage}, dec: {return --storage})
}
 
let c = CounterCreator(10)
 
c.inc() // 11
c.inc() // 12
c.dec() // 11

Using the explicit return for one line expressions, you can remove the returns from the closures

return Counter(inc: {++storage}, dec: {--storage})

Disregard this, here's a better version: https://gist.github.com/narfdotpl/838db18ea43f71c63b23