Swift is still very new, but all kinds of interesting libraries are being created around it. Dollar is a great example, providing useful functional programming language helpers. There are 2 parts to the library — Dollar is purely functional and Cent includes extension to built-in classes. The GitHub repository has many examples, but here's a few highlights:

    $.difference([1, 2, 3, 4, 5], [5, 2, 10]) 
    > [1, 3, 4]

    $.flatten([[[3], 4], 5]) as Int[] 
    > [3, 4, 5]

    let arr = [["age": 20], ["age": 30], ["age": 40]]
    $.pluck(arr, value: "age") 
    > [20, 30, 40]

    let fibMemo = $.memoize { (fib: (Int -> Int), val: Int) -> Int in
      return val == 1 || val == 0 ? 1 : fib(val - 1) + fib(val - 2)
    }
    let x = fibMemo(5)

    var beatle = Car(name: "Fusca")
    $.tap(beatle, {$0.name = "Beatle"}).color = "Blue"