我來了泣港，swift
定義
用于做值類型對(duì)比的協(xié)議。
適用范圍
遵循Equatable的類型都可以使用==或是!=符號(hào)對(duì)比判斷居暖。這個(gè)類型包括struct/class/enum
實(shí)現(xiàn)原理
任何遵循Equatable的類型子刮，都需要實(shí)現(xiàn)方法static func ==(lhs: Self, rhs: Self) -> Bool在這個(gè)方法內(nèi)按照指定的值和值間對(duì)比關(guān)系返回true或是false，外部表現(xiàn)為==或是!=的結(jié)果
struct Human: Equatable {
var name: String
var age = 5
static func == (lhs: Self, rhs: Self) -> Bool {
return lhs.name == rhs.name
}
}
let tom = Human(name: "tom", age: 5)
let tim = Human(name: "tim", age: 6)
tom == tim // false
let man1 = Human(name: "tom", age: 5)
let man2 = Human(name: "tom", age: 6)
man1 == man2 // true
Human對(duì)Equatable方法定義為只判斷name屬性是否值相同煌恢，即使age屬性不同，man1==man2結(jié)果是true
在不同類型中的差異
- class遵循Equatable必須要實(shí)現(xiàn)
static func ==(lhs: Self, rhs: Self) -> Bool方法震庭。但是瑰抵，struct遵循Equatable可以不用實(shí)現(xiàn)static func ==(lhs: Self, rhs: Self) -> Bool方法，默認(rèn)將struct實(shí)例中所有屬性對(duì)比并返回與結(jié)果
struct Dog: Equatable {
var name: String
var age = 0
}
let dog1 = Dog(name: "tom", age: 1)
let dog2 = Dog(name: "tom", age: 1)
dog1 == dog2 // true
let dog3 = Dog(name: "tom", age: 1)
let dog4 = Dog(name: "tom", age: 2)
dog3 == dog4 // false
struct Dog遵循Equatable協(xié)議但沒有實(shí)現(xiàn)協(xié)議方法其實(shí)例dog1與dog2實(shí)例相等归薛，dog3與dog3實(shí)例不相等
- 數(shù)組等容器類（數(shù)組/字典等）內(nèi)部的元素需要遵循Equatable才能實(shí)現(xiàn)一些能力，例如contains(_:)
let students = ["Kofi", "Abena", "Efua", "Kweku", "Akosua"]
let nameToCheck = "Kofi"
if students.contains(nameToCheck) {
print("\(nameToCheck) is signed up!") // Prints "Kofi is signed up!"
} else {
print("No record of \(nameToCheck).")
}
- swift standard library中的大部分基礎(chǔ)類型默認(rèn)已經(jīng)遵循Equatable匪蝙，例如Int/Array/Dictionary/Set
- struct重的屬性如果有不遵守Equatable主籍，那么其實(shí)例無法用
==
class MyClassNoEquatable {
}
struct NoEquatableStruct: Equatable {
var mc = MyClassNoEquatable()
}
let nes1 = NoEquatableStruct()
let nes2 = NoEquatableStruct()
nes1 == nes2
上面代碼會(huì)報(bào)錯(cuò)，提示Type 'NoEquatableStruct' does not conform to protocol 'Equatable'
協(xié)議間的關(guān)聯(lián)
Hashable協(xié)議基于Equatable協(xié)議逛球，對(duì)于struct遵守Hashable并不需要實(shí)現(xiàn)Equatable方法千元，但是對(duì)于class遵守Hashable必須要實(shí)現(xiàn)Equatable的方法
Comparable協(xié)議基于Equatable
==與===
- Equatable本質(zhì)是對(duì)屬性的值對(duì)比，適用范圍有struct/class/enum
-
===是對(duì)class實(shí)例指針的對(duì)比颤绕，且僅適用于class實(shí)例
class IntegerRef: Equatable {
let value: Int
init(_ value: Int) {
self.value = value
}
static func == (lhs: IntegerRef, rhs: IntegerRef) -> Bool {
return lhs.value == rhs.value
}
}
let a = IntegerRef(100)
let b = IntegerRef(100)
print(a == a, a == b, separator: ", ") // Prints "true, true"
let c = a
print(c === a, c === b, separator: ", ") // Prints "true, false"
