Playing with closure. Copy&paste in Playground

closureOne.swift

typealias closureType = (Int) -> (Int)

let ff = { return $0 * 2 }

let tt = { return $0 - ff($0) }

func ret(idx: Int, closure: closureType) -> NSNumber {
    return NSNumber(integer: closure(idx))
}

let _ = (0...100).map { return ret($0, closure: ff) }

let _ = (0...100).map { return ret($0, closure: tt) }

let mapFunc = [ff, tt] // var mapFunc = [closureType]()

let result = mapFunc.map { $0(1) }

struct Calculator: Operation {
    func ret(idx: Int, closure: closureType) -> NSNumber {
        return NSNumber(integer: closure(idx))
    }
}

Calculator().ret(1, closure: tt)