var v: UInt8 = UInt8.min
v -= 1

var v1 = UInt8.min
var v2 = v1 &- 1 //v2 = 255

var v1 = UInt8.max
var v2 = v1 &* 2 // 等價于 v1 &+ v1

struct Point {
    var x = 0, y = 0
    static func + (p1: Point, p2: Point) -> Point {
        Point(x: p1.x + p2.x, y: p1.y + p2.y)
    }
    static prefix func - (p: Point) -> Point {
        Point(x: -p.x, y: -p.y)
    }
    static func += (p1: inout Point, p2: Point) {
        p1 = p1 + p2
    }
    static postfix func ++ (p: inout Point) -> Point {
        let tmp = p
        p += Point(x: 1, y: 1)
        return tmp
    }
    static prefix func ++ (p: inout Point) -> Point {
        p += Point(x: 1, y: 1)
        return p
    }
}
var p1 = Point(x: 10, y: 20)
var p2 = Point(x: 11, y: 22)
let p3 = p1 + p2
let p4 = -p3
print(p4)

class Person: Equatable {
    var age: Int
    init(age: Int) {
        self.age = age
    }
    static func == (lhs: Person, rhs: Person) -> Bool {
        lhs.age == rhs.age
    }
}
var p1 = Person.init(age: 10)
var p2 = Person(age: 11)
print(p1 == p2)

enum Answer {
    case wrong
    case right
}
var s1 = Answer.wrong
var s2 = Answer.right
print(s1 == s2)

precedencegroup 優(yōu)先級組 {
    associativity: 結(jié)合性(left/right/none)
    higherThan: 比誰的優(yōu)先級高
    lowerThan: 比誰的優(yōu)先級低
    assignment: true代表在可選鏈操作中擁有跟賦值運(yùn)算符一樣的優(yōu)先級
}

prefix operator +++
prefix func +++ (_ i: inout Int) {
    i += 2
}
var age = 10
+++age

infix operator +-: PlusMinusPrecedence
precedencegroup PlusMinusPrecedence {
    associativity: none
    higherThan: AdditionPrecedence
    lowerThan: MultiplicationPrecedence
    assignment: true
}
struct Point {
    var x = 0, y = 0
 
    static func +- (p1: Point, p2: Point) -> Point {
        Point(x: p1.x + p2.x, y: p1.y - p2.y)
    }
}
class Person {
    var age = 0
    var point: Point = Point()
}
var p: Person? = Person()
p?.point +- Point(x: 10, y: 20)