swift -- Any、AnyObject、AnyClass、T.self、T.Type、is、as、as、Self

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Any

代表任意类型(枚举、结构体、类,也包括函数类型或者Optional类型)

var stu: Any = 10
// 创建1个能存放任意类型的数组
stu = "Jack"
stu = Student()

// 创建1个能存放任意类型的数组
// var data = Array<Any>()
var data = [Any]()
data.append(1)
data.append(3.14)
data.append(Student())
data.append("Jack")
data.append({ 10 })

AnyObject

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

  • 可以是instance 也可以是类

  • 在协议后面写上: class也代表只有类能遵守这个协议

var t = TGTeacher()
// AnyObject 表代是对象实例类型
var t1: AnyObject = t
// AnyObject 表代是TGTeacher类的类型
var t2: AnyObject = TGTeacher.self
protocol Runnable: AnyObject{}
class Person: Runnable {}

struct Student:Runnable {}
//报错: error: non-class type 'Student' cannot conform to class protocol 'Runnable'

AnyClass

代表任意实例的类型: AnyObject.Type

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

T.self

  • T.self是一个元类型(metadata)的指针,metadata存放着类型相关信息
  • 如果T是实例对象,返回的就是它本身; T是类,那么返回的是Metadata
class Person {}
class Student : Person {}
var perType: Person.Type = Person.self//perType Person前8个字节,存放这metadata地址值
var stuType: Student.Type = Student.self
perType = Student.self

T.Type

是一种类型,T.self属于T.Type类型

type(of:)

用来获取一个值的类型

var per = Person()
var perType = type(of: per) //取出person对象的前8个字节 即元类型 Person.self
print(Person.self == type(of: per)) // true

is

is用来判断是否为某种类型

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

as

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
(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]()
//类型一致的时候可以用as ,肯定可以转的时候
data. append(Int("123") as Any ) //数组里面可以添加可选项类型
var d=10 as Double
print(d) // 10.0

元类型的应用

  • 元类型创建对象
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]))

  • 元类型作为参数
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 

//从结果可以看得出来,Swift还有个隐藏的基类:Swift._SwiftObject 
//可以参考Swift源码:https://github.com/apple/swift/blob/master/stdlib/public/runtime/SwiftObject.h

Self

  • Self代表当前类型
class Person {
    var age = 1
    static var count = 2
    func run() {
        print(self.age) // 1
        print(Self.count) // 2
    }
}
  • 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()
// Person
print(p.test())
var stu = Student()
// Student
print(stu.test())