柯里化（Currying）

是把接受多个参数的函数变换成接受一个单一参数(最初函数的第一个参数)的函数，并且返回接受余下的参数且返回结果的新函数
swift 面试可能会这样考吧, 叫你写一个加数字的返回一个新的结果
如： 加1 加2 加3 加4 普遍会写四个函数么？
那么用柯里化得方式写一个就OK了,它允许把上次的结果作为返回一个新的函数结果

func addOne(_ num: Int) -> Int {
    return num + 1
}

func addTo(_ adder: Int) -> (Int) -> Int {
    return {
        num in
        return num + adder
    }
}

let addTwo = addTo(2)    //返回的两次  int的函数
let result = addTwo(6)   // result = 8



func greaterThan(_ comparer: Int) -> (Int) -> Bool {
    return { $0 > comparer }
}

let greaterThan10 = greaterThan(10);

greaterThan10(13)    // => true
greaterThan10(9)     // => false

protocol TargetAction {
    func performAction()
}

struct TargetActionWrapper<T: AnyObject>: TargetAction {
    weak var target: T?
    let action: (T) -> () -> ()
    func performAction() -> () {
        if let t = target {
            action(t)()
        }
    }
}

enum ControlEvent {
    case touchUpInside
    case valueChanged
    // ...
}


class Control {
  var actions = [ControlEvent: TargetAction]()
   func setTarget<T: AnyObject>(_ target: T, action: @escaping (T) -> () -> (), controlEvent: ControlEvent) {
            
            actions[controlEvent] = TargetActionWrapper(
                target: target, action: action)
    }
    
    func removeTargetForControlEvent(_ controlEvent: ControlEvent) {
        actions[controlEvent] = nil
    }
    func performActionForControlEvent(_ controlEvent: ControlEvent) {
        actions[controlEvent]?.performAction()
    }
}