Generator-scoped variables

genscoped-variables.swift

func anyGenerator<Element>(initial: Element, body: (inout Element) -> Element?) -> AnyGenerator<Element> {
    return {
        var i: Element? = initial

        return anyGenerator {
            var r: Element?
            if var x = i {
                r = body(&x)
                i = x
            }

            return r
        }
    }()
}


let naturalNumbers = anyGenerator(0) { (inout a: Int) in
    return a++
}

print(naturalNumbers.next()) // Prints Optional(0)
print(naturalNumbers.next()) // Prints Optional(1)