swift协议

协议

协议可以用来定义方法、属性、下标的声明,协议可以被枚举、结构体、类遵守(多个协议之间用逗号隔开)

协议中定义方法时不能有默认参数值

默认情况下,协议中定义的内容必须全部都实现

protocol Drawable {
    func draw() 
    var x: Int { get set } 
    var y: Int { get } 
    subscript(index: Int) -> Int { get set } 
}

协议中的属性

协议中定义属性时必须用var关键字

实现协议时的属性权限要不小于协议中定义的属性权限

协议定义get、set,用var存储属性或get、set计算属性去实现

协议定义get,用任何属性都可以实现

协议中static、class

为了保证通用,协议中必须用static定义类型方法、类型属性、类型下标。不能用class定义

protocol Drawable { static func draw() }

class Person1 : Drawable { 
  class func draw() { 
    print("Person1 draw") 
  } 
}

class Person2 : Drawable { 
  static func draw() { 
    print("Person2 draw") 
  } 
}

mutating

只有将协议中的实例方法标记为mutating

才允许结构体、枚举的具体实现修改自身内存

类在实现方法时不用加mutating,枚举、结构体才需要加mutating

protocol Drawable { 
  mutating func draw() 
}

class Size : Drawable { 
  var width: Int = 0 
  func draw() { 
    width = 10 
  } 
}

struct Point : Drawable {
  var x: Int = 0 
  mutating func draw() {
    x = 10
  }
}

init

协议中还可以定义初始化器init。非final类实现时必须加上required

protocol Drawable { init(x: Int, y: Int) }

class Point : Drawable { 
  required init(x: Int, y: Int) {} 
}

final class Size : Drawable { 
  init(x: Int, y: Int) {} 
}

如果协议实现的初始化器,刚好是重写了父类的指定初始化器 。那么这个初始化必须同时加required、override

protocol Livable { init(age: Int) }

class Person { 
  init(age: Int) {} 
}

class Student : Person, Livable { 
  required override init(age: Int) { 
    super.init(age: age) 
  } 
}

init、init?、init!

协议中定义的init?、init!,可以用init、init?、init!去实现

协议中定义的init,可以用init、init!去实现

protocol Livable { 
  init() 
  init?(age: Int) 
  init!(no: Int) 
}

class Person : Livable {
    required init() {} 
    //required init!() {}

    required init?(age: Int) {} 
  //required init!(age: Int) {} 
  //required init(age: Int) {}

    required init!(no: Int) {} 
  //required init?(no: Int) {} 
  //required init(no: Int) {}
}

协议的继承

一个协议可以继承其他协议

protocol Runnable { func run() }

protocol Livable : Runnable { func breath() }

class Person : Livable { 
    func breath() {} 
    func run() {} 
}

协议组合

协议组合,可以包含1个类类型(最多1个)

protocol Livable {} 
protocol Runnable {} 
class Person {}

// 接收Person或者其子类的实例 
func fn0(obj: Person) {} 
// 接收遵守Livable协议的实例 
func fn1(obj: Livable) {} 
// 接收同时遵守Livable、Runnable协议的实例 
func fn2(obj: Livable & Runnable) {} 
// 接收同时遵守Livable、Runnable协议、并且是Person或者其子类的实例 
func fn3(obj: Person & Livable & Runnable) {}

typealias RealPerson = Person & Livable & Runnable 
// 接收同时遵守Livable、Runnable协议、并且是Person或者其子类的实例 
func fn4(obj: RealPerson) {}

CaseIterable

让枚举遵守CaseIterable协议,可以实现遍历枚举值

enum Season : CaseIterable { 
    case spring, summer, autumn, winter 
} 
let seasons = Season.allCases 
print(seasons.count) // 4 
for season in seasons {
    print(season) 
} // spring summer autumn winter

CustomStringConvertible

遵守CustomStringConvertible、 CustomDebugStringConvertible协议,都可以自定义实例的打印字符串

print调用的是CustomStringConvertible协议的description

debugPrint、po调用的是CustomDebugStringConvertible协议的debugDescription

class Person : CustomStringConvertible, CustomDebugStringConvertible { 
  var age = 0 
  var description: String { "person_\(age)" } 
  var debugDescription: String { "debug_person_\(age)" } 
} 
var person = Person() 
print(person) // person_0 
debugPrint(person) // debug_person_0

Any、AnyObject

Swift提供了2种特殊的类型:Any、AnyObject

Any:可以代表任意类型(枚举、结构体、类,也包括函数类型)

AnyObject:可以代表任意类类型(在协议后面写上: AnyObject代表只有类能遵守这个协议)

在协议后面写上: class也代表只有类能遵守这个协议

is、as?、as!、as

is用来判断是否为某种类型,as用来做强制类型转换

protocol Runnable { 
  func run() 
} 
class Person {
  
} 
class Student : Person, Runnable { 
  func run() { print("Student run") } 
  func study() { print("Student study") }
}


var stu: Any = 10 
print(stu is Int) // true 
stu = "Jack" 
print(stu is String) // true
stu = Student() 
print(stu is Person) // true 
print(stu is Student) // true 
print(stu is Runnable) // true

var stu: Any = 10 
(stu as? Student)?.study() // 没有调用study 
stu = Student() 
(stu as? Student)?.study() // Student study 
(stu as! Student).study() // Student study
(stu as? Runnable)?.run() // Student run

var data = [Any]() 
data.append(Int("123") as Any)

var d = 10 as Double 
print(d) // 10.0

X.self、X.Type、AnyClass

X.self是一个元类型(metadata)的指针,metadata存放着类型相关信息

X.self属于X.Type类型

class Person {} 
class Student : Person {} 
var perType: Person.Type = Person.self 
var stuType: Student.Type = Student.self 
perType = Student.self

var anyType: AnyObject.Type = Person.self 
anyType = Student.self

public typealias AnyClass = AnyObject.Type 
var anyType2: AnyClass = Person.self 
anyType2 = Student.self

var per = Person() 
var perType = type(of: per) // Person.self 
print(Person.self == type(of: per)) // true

元类型的应用

class Animal { required init() {} } 
class Cat : Animal {} 
class Dog : Animal {} 
class Pig : Animal {}

func create(_ clses: [Animal.Type]) -> [Animal] { 
  var arr = [Animal]() 
  for cls in clses { 
    arr.append(cls.init()) 
  } 
  return arr 
}

print(create([Cat.self, Dog.self, Pig.self]))


import Foundation 
class Person {
  var age: Int = 0 
} 
class Student : Person {
  var no: Int = 0 
} 
print(class_getInstanceSize(Student.self)) // 32 
print(class_getSuperclass(Student.self)!) // Person 
print(class_getSuperclass(Person.self)!) // Swift._SwiftObject
// 由此可以看得出来,Swift还有个隐藏的基类:Swift._SwiftObject

Self

Self代表当前类型

Self一般用作返回值类型,限定返回值跟方法调用者必须是同一类型(也可以作为参数类型)

protocol Runnable { func test() -> Self } 
class Person : Runnable {
  required init() {}
  func test() -> Self { type(of: self).init() } 
} 
class Student : Person {}

var p = Person() 
print(p.test())// Person 

var stu = Student()  
print(stu.test())// Student

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