defer

• 将延迟至当前作用域结束之前执行
• throws、return之前会执行

fatalError

• 直接抛出错误，结束程序

溢出运算符Overflow Operator

&- 、 &+ 、&*

运算符重载

自定义运算符

中缀自定义

infix operator +-+ : AdditionPrecedence
struct Point  {
    var x : Int, y: Int
    static func +-+(left:Point,right:Point) -> Int {
        return (left.x+right.x)-(left.y+right.y)
    }
}

指针的pointee

获取指向某个变量的指针

获取指向堆空间实例的指针

通配符

重写switch case判断逻辑 （ ~= ）

条件编译

打印

参考：https://docs.swift.org/swift-book/ReferenceManual/Attributes.html

KVO KVC

• @objc dynamic 修饰对应属性 ```swift class WuObserver: NSObject {

  override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {

    print(change?[NSKeyValueChangeKey.oldKey]! )

  } } class People: NSObject {

  @objc dynamic var str = “init” var obs = WuObserver() var observation:NSKeyValueObservation?

  override init() {

    super.init()
    addObserver(obs, forKeyPath: "str", options: [.new,.old], context: nil)
    //或者通过block
    observation = observe(\People.str, options: .new, changeHandler: { (obser, change) in
        print(change,obser)
    })

  } }

<a name="aSnpq"></a>
# 利用关联对象，为class扩展储存属性
```swift
class People {}
extension People {
    private static var NAME_KEY: Void?
    var name : String {
        set {
            objc_setAssociatedObject(self, &People.NAME_KEY, newValue, .OBJC_ASSOCIATION_ASSIGN)
        }
        get {
            return (objc_getAssociatedObject(self, &People.NAME_KEY) as? String) ?? ""
        }
    }
}
let pp = People()
pp.name = "yuan"
print(pp.name)

多线程 加锁