var x = [1, 2, 3];

    let y = x.map( { v -> Int in
      print("got \(v)")
      x.removeAll()
      return 1
    })

    print("x: \(x)")
    print("y: \(y)")


    got 1
    got 2
    got 3
    x: []
    y: [1, 1, 1]

I don't know much about swift but this shows the closure is able to mutate the Array. I guess value types are captured by reference by a closure.