1.以下面代碼為情境代碼

class Shape{
    
}
class Circle:Shape{
    
}
class Rectangle:Shape{
    
}
var shape  = Shape()
var circle = Circle()
var rect = Rectangle()
var array = Array<Any>()
array.append(circle)
array.append(shape)
array.append(rect)
array.append("aaaa")
array.append({return "aaaaa"})

2.is 用來(lái)判斷對(duì)象是否屬于某個(gè)類或者其子類,相當(dāng)于OC中的isKindOf方法

for item in array{
    if item is Rectangle{
        print("Rectangle:\(item)")
    }else if item is Circle{
        print("Circle:\(item)")
    }
    
}

3.as as? as! 轉(zhuǎn)換

• as? 轉(zhuǎn)換成功之后是一個(gè)optional類型的值,轉(zhuǎn)換失敗為nil

let s1 = shape as? Circle
s1.dynamicType

• as! 轉(zhuǎn)換成功后是原類型不是目標(biāo)類型，轉(zhuǎn)換失敗報(bào)錯(cuò)

let s2 = array.first as! Shape
s2.dynamicType   //Circle.Type
//let s3 = array.first as! Rectangle //報(bào)錯(cuò)

• as 當(dāng)編譯器也知道一定能轉(zhuǎn)成功的時(shí)候可以用as

//方式一
let s4 = shape as Shape
s4.dynamicType
//方式二
for item in array{
    switch item {
    case is Circle:
        print("circle")
    case is Rectangle:
        print("rectangle")
    case let s3 as Shape:
        print(s3)
    default:
        break
    }
}