Swift:在switch语句中测试类类型

时间:2014-09-08 12:41:51

标签: class swift switch-statement

在Swift中,您可以使用“is”检查对象的类类型。如何将其合并到“开关”块中?

我认为这是不可能的,所以我想知道最好的方法是什么。

TIA, 彼得。

3 个答案:

答案 0 :(得分:362)

您绝对可以在is块中使用switch。请参阅"类型转换为Any和AnyObject"在Swift编程语言中(虽然它当然不限于Any)。他们有一个广泛的例子:

for thing in things {
    switch thing {
    case 0 as Int:
        println("zero as an Int")
    case 0 as Double:
        println("zero as a Double")
    case let someInt as Int:
        println("an integer value of \(someInt)")
    case let someDouble as Double where someDouble > 0:
        println("a positive double value of \(someDouble)")
// here it comes:
    case is Double:
        println("some other double value that I don't want to print")
    case let someString as String:
        println("a string value of \"\(someString)\"")
    case let (x, y) as (Double, Double):
        println("an (x, y) point at \(x), \(y)")
    case let movie as Movie:
        println("a movie called '\(movie.name)', dir. \(movie.director)")
    default:
        println("something else")
    }
}

答案 1 :(得分:21)

如果您没有值,只需要任何对象:

  

swift 4

func test(_ val:Any) {
    switch val {
    case is NSString:
        print("it is NSString")
    case is String:
        print("it is a String")
    case is Int:
        print("it is Int")
    default:
        print(val)
    }
}


let str: NSString = "some nsstring value"
let i:Int=1
test(str) // it is NSString
test(i) // it is Int

答案 2 :(得分:6)

我喜欢这种语法:

switch thing {
case _ as Int: print("thing is Int")
case _ as Double: print("thing is Double")
}

因为它使您可以快速扩展功能,如下所示:

switch thing {
case let myInt as Int: print("\(myInt) is Int")
case _ as Double: print("thing is Double")
}