Swift运算符使用方法浅析

溢出运算符(Overflow Operator)

1、Swift的算数运算符出现溢出时会抛出运行时错误

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

2、Swift有溢出运算符(&+、&-、&*),用来支持溢出运算

var v1 = UInt8.min
var v2 = v1 &- 1 //v2 = 255
var v1 = UInt8.max
var v2 = v1 &* 2 // 等价于 v1 &+ v1

运算符重载(Operator Overload)

1、类、结构体、枚举可以为现有的运算符提供自定义的实现,这个操作叫做:运算符重载

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)

Equatable

1、要想得知2个实例是否等价,一般做法是遵守Equatable协议,重载 == 运算符

与此同时,等价于重载了 != 运算符

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)

2、Swift为以下类型提供默认的Equatable实现

没有关联类型的枚举

只拥有遵守Equatable协议关联类型的枚举

只拥有遵守Equatable协议存储属性的结构体

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

3、引用类型比较存储的地址值是否相等(是否引用着同一个对象),使用恒等运算符 === 、!==

Comparable

1、要想比较2个实例的大小,一般做法是:遵守Comparable协议,重载相应的运算符

自定义运算符 (Custom Operator)

1、可以自定义新的运算符:在全局作用域使用operator进行声明

prefix operator 前缀运算符
postfix operator 后缀运算符
infix operator 中缀运算符:优先级组

precedencegroup 优先级组 {
    associativity: 结合性(left/right/none)
    higherThan: 比谁的优先级高
    lowerThan: 比谁的优先级低
    assignment: true代表在可选链操作中拥有跟赋值运算符一样的优先级
}
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)
作者:扑腾的蛾子 原文地址:https://blog.csdn.net/run_in_road/article/details/126551296

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