subscript mutation example

subscript.swift

extension Int {
    mutating func increment() {
        self = self.successor()
    }
}

struct S {
    var x: Int = 0
    subscript()->Int {
        get {
            println("getting x: x is \(x)")
            return x
        }
        set(newVal) {
            println("setting x to \(newVal)")
            x = newVal
        }
    }
}

var s = S()
s[].increment()


func f(inout i: Int) {
    println("i is \(i)")
    println("about to set i to 42")
    i = 42
    println("about to set i to 100")
    i = 100
    println("about to exit f()")
    // note, only on exit will the 
    // subscript set be called
}

f(&s[])